Method and device for performing handover in mobile communication system

ABSTRACT

A method for transmitting a channel state by a terminal in a communication system, according to one embodiment, comprises the steps of: receiving discontinuous reception (DRX) configuration information from a base station; determining whether the terminal is set to transmit channel state information only in onDuration according to a DRX operation; determining whether an arbitrary subframe to be received is a subframe included in onDuration if the terminal is set to transmit the channel state information only in onDuration according to the configuration; and not transmitting the channel state information on the arbitrary subframe if the arbitrary subframe is not a subframe included in onDuration. According to the embodiment, the terminal can efficiently report channel state information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/726,113,filed Dec. 23, 2019, which is a continuation of application Ser. No.15/168,173, filed May 30, 2016, now U.S. Pat. No. 10,517,025, which is acontinuation of application Ser. No. 14/421,794, now U.S. Pat. No.9,357,446, which is the 371 National Stage of International ApplicationNo. PCT/KR2013/007359, filed Aug. 14, 2013, which claims priority toKorean Patent Application Nos. 10-2012-0088995, filed Aug. 14, 2012,10-2012-0109172, filed Sep. 28, 2012, 10-2012-0111951, filed Oct. 9,2012, 10-2012-0123712, filed Nov. 2, 2012, and 10-2012-0127549, filedNov. 12, 2012, the disclosures of which are incorporated herein byreference into the present disclosure as if fully set forth herein.

BACKGROUND 1. Field

The present disclosure relates to a handover method and apparatus foruse in a mobile communication system.

2. Description of Related Art

Mobile communication systems were developed to provide mobile users withcommunication services. With the rapid advance of technologies, themobile communication systems have evolved to the level capable ofproviding high speed data communication service beyond the earlyvoice-oriented services.

Recently, standardization for a Long Term Evolution (LTE) system, as oneof the next-generation mobile communication systems, is underway in the3rd Generation Partnership Project (3GPP). LTE is a technology designedto provide high speed packet-based communication of up to 100 Mbps andits standardization is completed almost currently.

In the mobile communication system, supporting mobility is one of thesignificant issues. Particularly when the terminal is handed over to acell which is interfered by neighbor cells significantly, the handoveris likely to fail due to the failure of acquiring correct informationfrom the target cell.

SUMMARY

The present invention aims to provide a method and apparatus forfacilitating acquisition of information from the target cells even whenthe terminal undergoes significant interference from neighboring cellsin the course of handover.

In accordance with an aspect of the present invention, a channel statetransmission method of a terminal in a communication system includesreceiving Discontinuous Reception (DRX) configuration information from abase station, determining whether the DRX configuration instructs totransmit channel state information only in an on-duration (onDuration)of DRX operation, determining, when the DRX configuration instructs totransmit channel state information only in the onDuration of DRXoperation, a subframe to arrive is included in the onDuration, andskipping, when the subframe is not included in the onDuration,transmission of the channel state information in the subframe.

In accordance with another aspect of the present invention, a terminalfor transmitting channel state in a communication system includes atransceiver which transmits and receives to and from a base station anda control unit which controls receiving Discontinuous Reception (DRX)configuration information from the base station, determines whether theDRX configuration instructs to transmit channel state information onlyin an on-duration (onDuration) of DRX operation, determines, when theDRX configuration instructs to transmit channel state information onlyin the onDuration of DRX operation, a subframe to arrive is included inthe onDuration, and controls skipping, when the subframe is not includedin the onDuration, transmission of the channel state information in thesubframe.

The present invention is advantageous in that the terminal is capable ofreporting channel state information efficiently.

Also, the present invention is advantageous in terms of facilitatinghandover to a target cell undergoing significant interference fromneighboring cells by providing the information inevitable for thehandover operation of the target cell.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating LTE system architecture to which thepresent invention is applied.

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied.

FIG. 3 is a flowchart illustrating the UE operation according to thefirst embodiment.

FIG. 4 is a diagram illustrating a System Frame Number (SFN) offset.

FIG. 5 is a flowchart illustrating another UE operation according to thefirst embodiment.

FIG. 6 is a diagram illustrating uplink transmission in the LTE system.

FIG. 7 is a diagram illustrating uplink transmission on the time axis inthe LTE system.

FIG. 8 is a flowchart illustrating the UE operation according to thesecond embodiment.

FIG. 9 is a flowchart illustrating another UE operation according to thesecond embodiment.

FIG. 10 is a flowchart illustrating another UE operation according tothe second embodiment.

FIG. 11 is a diagram illustrating the carrier aggregation.

FIG. 12 is a flowchart illustrating the UE operation according to thethird embodiment.

FIG. 13 is a flowchart illustrating the UE operation according to thefourth embodiment.

FIG. 14 is a block diagram illustrating a configuration of the UEaccording to an embodiment of the present invention.

FIG. 15 is a block diagram illustrating a configuration of the eNBaccording to an embodiment of the present invention.

FIG. 16 is a flowchart illustrating another UE operation according tothe second embodiment.

FIG. 17 is a signal flow diagram illustrating a procedure of protectingagainst data loss using PDCP STATUS REPORT.

FIG. 18 is a flowchart illustrating a PDCP transmission entity operationaccording to the fifth embodiment.

FIG. 19 is a flowchart illustrating another UE operation according tothe fifth embodiment.

FIG. 20 is a flowchart illustrating the UE operation according to thesixth embodiment.

FIG. 21 is a diagram illustrating the normal DRX operation.

FIG. 22 is a flowchart illustrating the UE operation of determiningwhether to transmit CQI according to the fifth embodiment.

FIG. 23 is a flowchart illustrating the UE operation of determiningwhether to transmit SRS according to the fifth embodiment.

FIG. 24 is a diagram illustrating SRS transmission.

FIG. 25 is a flowchart illustrating another UE operation of determiningwhether to transmit CQI according to the seventh embodiment.

FIG. 26 is a flowchart illustrating another UE operation of determiningwhether to transmit SRS according to the seventh embodiment.

FIG. 27 is a diagram illustrating a scenario related to the cellinformation selectedUTRA-CellID.

FIG. 28 is a signal flow diagram illustrating a procedure of includingthe cell information selectedUTRA-CellID.

FIG. 29 is a flowchart illustrating the UE operation of including thecell information selectedUTRA-CellID.

FIG. 30 is a diagram illustrating a scenario related to the cellinformation previousUTRA-CellID.

FIG. 31 is a signal flow diagram illustrating a procedure of includingthe cell information previousUTRA-CellID.

FIG. 32 is a flowchart illustrating the UE operation of including thecell information previousUTRA-CellID.

FIG. 33 is a flowchart illustrating another UE operation of determiningwhether to transmit CQI according to the seventh embodiment.

FIG. 34 is a flowchart illustrating another UE operation of determiningwhether to transmit CQI according to the seventh embodiment.

FIG. 35 is a flowchart illustrating the UE operation procedure accordingto another embodiment of the present invention.

FIG. 36 is a flowchart illustrating a method of adjusting the variablesrelated to the uplink transmission of the UE.

FIG. 37 is a flowchart illustrating the UE operation related to theactivation of the SCell configured on the same frequency band as thePCell.

FIG. 38 is a flowchart illustrating the UE operation procedure accordingto another embodiment of the present invention.

DETAILED DESCRIPTION

In the following, detailed description of well-known functions andstructures incorporated herein may be omitted to avoid obscuring thesubject matter of the present invention. Exemplary embodiments of thepresent invention are described with reference to the accompanyingdrawings in detail. A description is made of the LTE system and carrieraggregation briefly before explaining the present invention.

FIG. 1 is a diagram illustrating LTE system architecture to which thepresent invention is applied.

Referring to FIG. 1, the radio access network of the mobilecommunication system includes evolved Node Bs (eNBs) 105, 110, 115, and120, a Mobility Management Entity (MME) 125, and a Serving-Gateway(S-GW) 130. The User Equipment (hereinafter, referred to as UE) 135connects to an external network via eNBs 105, 110, 115, and 120 and theS-GW 130.

In FIG. 1, the eNBs 105, 110, 115, and 120 correspond to the legacy nodeBs of the UMTS system. The eNBs allow the UE 135 to establish a radiochannel and are responsible for complicated functions as compared to thelegacy node B. In the LTE system, all the user traffic including realtime services such as Voice over Internet Protocol (VoIP) are providedthrough a shared channel and thus there is a need of a device which islocated in the eNB to schedule data based on the state information suchas buffer states, power headroom states, and channel states of the UEs.Typically, one eNB controls a plurality of cells. In order to secure thedata rate of up to 100 Mbps, the LTE system adopts Orthogonal FrequencyDivision Multiplexing (OFDM) as a radio access technology. Also, the LTEsystem adopts Adaptive Modulation and Coding (AMC) to determine themodulation scheme and channel coding rate in adaptation to the channelcondition of the UE. The S-GW 130 is an entity to provide data bearersso as to establish and release data bearers under the control of the MME125. The MME 125 is responsible for mobility management of UEs andvarious control functions and may be connected to a plurality of eNBs.

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied.

Referring to FIG. 2, the protocol stack of the LTE system includesPacket Data Convergence Protocol (PDCP) 205 and 240, Radio Link Control(RLC) 210 and 235, Medium Access Control (MAC) 215 and 230, and Physical(PHY) 220 and 225. The PDCP 205 and 240 is responsible for IP headercompression/decompression, and the RLC 210 and 235 is responsible forsegmenting the PDCP Protocol Data Unit (PDU) into segments inappropriate size for Automatic Repeat Request (ARQ) operation. The MAC215 and 230 is responsible for establishing connection to a plurality ofRLC entities so as to multiplex the RLC PDUs into MAC PDUs anddemultiplex the MAC PDUs into RLC PDUs. The PHY 220 and 225 performschannel coding on the MAC PDU and modulates the MAC PDU into OFDMsymbols to transmit over radio channel or performs demodulating andchannel-decoding on the received OFDM symbols and delivers the decodeddata to the upper layer.

When the UE is handed over from a cell A to another cell B, the eNBsends the UE a dedicated RRC control message including partial systeminformation of the cell B in order to negate direct acquisition of thesystem information of the cell B at the UE. For example, the UE receivesthe Master Information Block (MIB), System Information Block (SIB) 1 andSIB 2 with the exception of SFN information. After handover to thetarget cell, the UE communicates with the target cell using the systeminformation received in advance and checks SFN of the cell based on theMIB received at an appropriate time.

If the cell B is a pico cell and experiencing severe interference fromthe cell A, it is difficult for the UE to acquire the MIB of the targetcell after handover to the cell B. This situation may continue until theUE move from the location where the handover is triggered to the cellcenter and thus the UE operate incorrectly without information.

FIG. 3 is a flowchart illustrating the UE operation according to thefirst embodiment. FIG. 4 is a diagram illustrating the SFN offset.

In the embodiment of FIGS. 3 and 4, the SFN offset between the sourceand target cells is sent to the UE such that the UE operates correctlybased thereon even when it fails to acquire the SFN from the target.

The UE operation is described hereinafter.

The UE receives an RRC control message commanding handover from an eNBat step 305.

The UE acquires downlink synchronization with the target cell andperform a random access procedure based on the information included inthe RRC control message at step 310.

The UE determines whether the RRC control message includes SFN offsetinformation at step 315. If so, the procedure goes to step 325 and,otherwise, step 320.

If the handover to the target cell is completed, the UE sends the targetcell a handover complete message and performs an MIP acquisitionprocedure to acquire SFN of the target cell at step 320. That is, the UEreceives and decodes the MIB at the first subframe of every radio frameby applying a predetermined MCS on predetermined frequency resource(e.g. center frequency resource). If the MIB is decoded successfully,the UE applies the MSB 10 bit of the SFN indicated by the MIB todetermine the SFN of the current radio frame.

At step 325, the UE determines whether the SFN of the target cell isacquired. For example, the UE may have acquired SFN already during themeasurement on the target cell before the handover. If the SFN has beenacquired already, the UE ignores the SFN offset information anddetermines the SFN of the current cell by applying the previouslyacquired SFN information at step 330. If the handover is completed, theUE sends the target cell a control message notifying that the handoveris completed successfully. Otherwise if no SFN has been acquired, the UEcalculates the SFN of the current cell by applying the SFN offsetinformation at step 335. The SFN offset information includes the firstinformation indicating the difference between the SFNs of the referencecell and the target cell and the second information indicating thedifference between the subframe 0 of the reference cell and the subframe0 of the target cell. The SFN of the target cell to be used foracquiring the first information may be the SFN of the radio frame whichis later in time than but closest to the radio frame of the referencecell among the radio frames of the target cell. Also, it may be the SFNof the radio frame which is earlier in time than but closest to theradio frame of the reference cell. For example, if there are the radioframes 410 and 415 of the neighbor target cell which are close in timeto the radio frame 405 of the reference cell, the first information isthe difference between the SFNs of the radio frames 405 and 415, i.e.,y-x.

The second information is the difference between a predeterminedsubframe of the reference cell and a predetermined subframe of thetarget cell, i.e., the difference between the 0th subframes as denotedby reference number 420.

The UE maintains the radio frame boundary and SFN of the source celluntil the handover to the target cell is completed, identifies the radioframe boundary of the target cell ager the handover to the target cellis completed, and adds the first information to the SFN of the radioframe of the source cell which precedes and is closest to the radioframe boundary to acquire the SFN.

Also, the UE may identify the subframe boundary of the target cell andthe radio frame boundary of the frame including the subframe by applyingthe first and second information to calculate the SFN of the radioframe.

In order to check the SFN offsets of the neighbor cells, the eNB maycommand the UE to measure the SFN offset. The reason for checking theSFN offsets of the neighboring cells is because the UE cannot acquirethe MIB at the cell boundary area of the neighboring cell due to thesevere interference of the neighboring cells. Accordingly, in order toacquire the SFN offset associated with the cell (e.g., pico cell) fromwhich it is difficult to acquire MIB due to the interference, the eNBinstructs the UE located in a cell having the center frequency differentfrom the center frequency of the pico cell to acquire the SFN offset.This is because the UE is capable of approaching the center of the picocell to acquire the SFN offset while maintain the connection with thecurrent cell.

In order to accomplish this, a Self-Organized Network (SON) is used inthe present invention. In SON, if an unknown cell is found around, theeNB instructs the UE to report the cell Global Identifier (CG) of thecell, and the UE tries to receive the SIB1 of the corresponding cellduring a predetermined period (hereinafter, T321). If the SIB1 isreceived successfully, the UE report the CGI information and PLMNidentifier included in the SIB1 to the eNB.

In the present invention, the eNB instructs the UE to SFN offset alongwith report CGI. The T321 is applied differently depending on whetherthe SFN offset report is configured or not such that the user measurethe SFN offset more correctly.

FIG. 5 is a flowchart illustrating another UE operation according to thefirst embodiment.

Referring to FIG. 5, the UE receives measurement configurationinformation (measConfig) form the eNB at step 505. The measurementconfiguration information includes measurement target and measurementreport trigger information. The measurement target information includescenter frequency information and physical cell identifier (PCI), and themeasurement report trigger information includes the information onwhether the measurement is event-driven, periodic, or upon receipt ofthe information such as CGI information which the eNB commands toreceive.

The UE determines whether the measurement configuration informationincludes the trigger type set to ‘periodic’ and the purpose set to ‘CGIreport’ at step 510. If the information is not included, the UE performsmeasurement and reports measurement result according to the legacytechnology at step 515. If the information is included, the UEdetermines whether the SFN offset report is indicated at step 520. Ifthe SFN offset report is indicated, the procedure goes to step 530 and,otherwise, step 525.

At step 525, the UE sets the T321 to an appropriate value according tocondition 1.

[Condition 1]

If an autonomous gap for use in measurement is indicated, the UE setsthe T321 to value 2 and, otherwise, value 3.

The autonomous gap is of generating and using a gap (time duration formuting transmission/reception) arbitrarily for the UE to performmeasurement without acceptance of the eNB. In the case of using theautonomous gap, it is preferred to set the T321 to a small value toavoid communication failure between the UE and the eNB. That is, thevalue 2 has to be less than the value 3.

The UE tries to acquire the SIB1 of the cell identified with the PCI andthe indicated center frequency until the T321 expires. If the SIB1 isacquired before expiry of the T321, the UE sends the eNB a predeterminedRRC control message including the CGI and PLMN identifier included inthe SIB1. If it fails to acquire the information before expiry of theT321, the UE sends the eNB a predetermined RRC control message includingthe information acquired successfully.

The UE sets the T321 to a predetermined value 1 at step 530. The UEtries to acquire the MIB and SIB1 of the cell identified with the PCIand indicated center frequency before expiry of the T321. If the MIB andSIB1 are acquired before expiry of the T321, the UE calculates the SFNoffset between the current serving cell and the target cell using theSFN information of the target cell which is acquired from the MIB. Next,the UE sends the eNB a predetermined RRC control message including theSFN offset and the CGI and PLMN identifier of the target cell. If theabove information is not acquired before expiry of the T321, the UEsends the eNB a predetermined RRC control message including theinformation acquired successfully.

When the UE is handed over from a macro cell to a pico cell, if may bedifficult to receive the SIB1. Unlike MIB, since the SIB1 is transmittedon the frequency resource varying dynamically, it is impossible to applyan interference cancellation scheme and this may result in a severeproblem. The SIB1 carries scheduling information of other systeminformation or TDD configuration information. Accordingly, if the UEfails to receive the SIB1 correctly, it may be difficult to receiveother system information.

In the present invention, if the UE is handed over to a pico cell inwhich it may be difficult to receive the SIB1, a dedicated RRC controlmessage is used for the source cell to provide the UE the SIB1information. Even when the system information is modified after the UE'shandover to the pico cell, the SIB1 information is provided through thededicated RRC control message.

From the viewpoint of the eNB, although the SIB1 is provided to the UEexperiencing severe interference from the current macro cell through thededicated control message, it is possible to provide the other UEs withthe SIB1 by applying a normal system information modification procedure.That is, the UE which receives the SIB1 through the dedicated controlmessage also may receive the paging information notifying of themodification of the system information. According to the conventionaltechnology, the UE which has received the above information determineswhether it is necessary to receive the modified system information basedon the SIB1 received through a common channel. The UE which receives theSIB1 through the dedicated control message is likely to be in anenvironment difficult to receive the SIB1 through the common channel andthus it is likely to be useless for the UE to try to receive the SIB1,resulting in unnecessary battery consumption. In order to solve thisproblem, if the SIB1 or control information included in the SIB1 isreceived through the dedicated control message, the UE assumes thatthere is no need of receiving the SIB1 through the common channel duringa predetermined period in the present invention. The SIB1 transmittedthrough the dedicated control message is referred to as dedicated SIB1,and the SIB1 transmitted through the common channel is referred to ascommon SIB1. The dedicated SIB1 may include part of the informationcarried in the common SIB1 but the included information is identicalwith that of the common SIB1.

FIG. 38 shows the UE operation.

The UE receives systemInfoModification at step 3805. ThesystemInfoModification is the control information notifying the UE ofthe modification of the system information and transmitted to the UEthrough the paging message. The UE in the connected state receives thepaging message at least once at a predetermined interval to detect thesystemInfoModification.

The UE determines whether the dedicated SIB1 has been received in x msbefore the receipt of the paging message at step 3810. The dedicatedSIB1 is transmitted from the eNB to the UE through the dedicated RRCcontrol message and includes predetermined control information as a partof the original system information. The dedicated SIB1 may include theinformation as follows.

-   -   System information scheduling information: Information        indicating the interval and time period of transmission of        system information.    -   value tag: Integer incrementing by 1 whenever the system        information is modified. The UE determines whether to receive        the modified system information by referencing the value tag.    -   TDD configuration information: Information provided when the        corresponding cell is the cell operating in TDD. This is a        predetermined integer indicating a pattern of downlink and        uplink subframes.

If the dedicated SIB1 has been received in the previous x ms, this meansthat the UE has performed the new system information acquisitionprocedure already based on the dedicated SIB1, the UE ignores thereceived systemInfoModification at step 3815. That is, the UE does notattempt receiving the common SIB1. Otherwise if the dedicated SIB1 hasnot been received in the previous x ms, the procedure goes to step 3820.

At step 3820, the UE determines whether the dedicated SIB1 is receivedbefore the next modification period starts. If the dedicated SIB1 is notreceived before the start of the next modification period, the UE startsa system information acquisition procedure from the start time of thenext modification period at step 3830. That is, the UE tries to receivethe common SIB1 at the start time of the next modification period and,if the common SIB2 is received, determines whether the rest systeminformation is received by referencing the value tag. If the dedicatedSIB1 is received in the middle of attempting to receive the common SIB1,the UE stops attempting receipt of the common SIB1, determines whetherto receive the rest system information by referencing the value tag ofthe dedicated SIB1, and checks the time duration for receiving the restsystem information. The modification period means the minimum period inwhich the system information can be modified. That is, the systeminformation may be modified typically at the start time of themodification period but not in the modification period. This is forallowing a plurality UEs to apply the newly modified system informationsimultaneously.

If the procedure goes to step 3825, this means that the UE has receivedthe dedicated SIB1 before the start of the next modification period. IfUE postpones the application of the dedicated SIB1 to the nextmodification period, this may affect bad influence to the system. Forexample, if the modified system information is the TDD configurationinformation and if the UE uses the old TDD configuration information tothe next modification period, severe interference may occur.Accordingly, upon receipt of the dedicated SIB1, the UE applies thededicated SIB1 immediately unlike the normal system informationmodification procedure. For example, the UE determines whether toacquire the rest system information by referencing the value tag and, ifit is necessary to receive the rest system information, starts theprocedure for acquiring the rest system information immediately. At thistime, although the system information is acquired wholly in the currentmodification period, the UE receives the system information in the nextmodification period again to prepare for the modification of the restsystem information in the next modification period. Also, if thededicated SIB1 is received, the UE may apply the control information,e.g. TDD configuration, included in the SIB1 immediately but the valuetag to the next modification period. In this case, the UE starts therest system information acquisition at the start time of the nextmodification period.

If it is determined to modify the system information in the [n+1]thmodification period, the eNB has to send the UE the dedicated SIB1before the start of the [n+1]th modification period. However, thededicated SIB1 may be transmitted even when the dedicated SIB1 istransmitted to the UE after the start of the [n+1]th modification perioddue to the retransmission on the RLC layer. In order to prepare for sucha case, if the dedicated SIB1 is received in the mth modificationperiod, the UE determines whether the value tag of the SIB1 is differentfrom the value tag received most recently (or value tag stored in theUE). if the tow values mismatch, this means that it is necessary toacquire the system information, and thus the UE receives predeterminedsystem information, e.g. SIB2, immediately by referencing the systeminformation scheduling information included in the dedicated SIB1.Although the rest system information is received successfully before theend of the mth modification period, the UE receives the rest systeminformation one more time in the [m+1]th to apply the system informationreceived in the [m+1]th or later finally. Accordingly, the rest systeminformation received in the mth modification period is applied untilreceiving the rest system information again in the [m+1]th modificationperiod or later, and the rest system information received in the [m+1]thmodification period or later is applied finally. The rest systeminformation means the system information which the UE in the connectedstate has to receive with the exception of the SIB1.

Second Embodiment

In order to accomplish the above objective, the LTE mobile communicationsystem adopts Discontinuous Reception operation which allows the UE totransmit uplink control signal only in the active time to minimize UEpower consumption. However, the current discontinuous receptionoperation is inefficient for the service generating uplink dataperiodically such as VoIP.

This is because the UE has to check PDCCH at every 8 ms per HARQ processto determine whether to apply adaptive retransmission.

FIG. 6 is a diagram illustrating uplink transmission in the LTE system.

Referring to FIG. 6, the uplink transmission resource is thefrequency/time resource. In the LTE mobile communication system, theunit transmission resource is defined by a frequency band having apredetermined width during a timeslot having a predetermined length. Oneregular quadrilateral denotes the unit transmission resource, and theunit transmission resource is referred to as resource block. Theresource block is 1 msec on the time axis and referred to as subframe orTransmission Time Interval (TTI).

The eNB scheduler allocates the UE the uplink transmission resourcethrough a control channel called Physical Downlink Control Channel(PDCCH), and the allocated transmission resource can be used fortransmitting and retransmitting the same packet at an interval of HARQRound Trip Time (RTT) 610 on the time axis.

The UE performs initial transmission of uplink data through theallocated transmission resource 620 and analyzes the HARQ feedbackinformation received at a predetermined time to determine whether toperform HARQ retransmission. if the HARQ feedback information is HARQNegative Acknowledgement (NACK) as denoted by reference number 645, theUE retransmits the data using the same transmission resource 625 at thenext HARQ transmission timing. The data retransmission is repeated untilthe HARQ ACK is received. That is, if the HARQ feedback information isHARQ NACK as denoted by reference number 650, the UE retransmits thedata using the same transmission resource 330 at the next HARQretransmission timing.

Afterward, if the HARQ ACK is received as denoted by reference number655, the uplink data transmission procedure ends. As described above, inthe synchronous HARQ process, if the HARQ NACK is received, the uplinktransmission resource is allowed automatically. Since it is notpreferred to transmit the same data over a predetermined number of timesin view of transmission efficiency, the maximum number ofretransmissions is limited. For example, if the maximum number ofretransmissions is set to 3, the UE determine the transmission resourceis invalid after three retransmissions although the HARQ ACK is notreceived. If the HARQ NACK is received repeatedly on the transmissionresources 625, 630, and 635, the UE determines that the transmissionresource 640 is invalid after the last retransmission 635 which isdetermined based on the maximum number of retransmissions and discardsthe data stored in the buffer. The initial transmission andretransmission are performed in the same HARQ process. The HARQ processincludes the soft buffer for buffering the HARQ data, and thetransmitter stores the data to be transmitted and the receiver storesthe received data. If the retransmitted data is received in a certainHARQ process, the data stored in the process and the receivedretransmission data re soft-combined. The HARQ process is allocated anidentifier. In the synchronous HARQ, the HARQ process identifiercorresponds to the data transmission/reception time one by one, and thetransmission and the retransmission are performed always in theprocessing indicated by the same identifier. For example, the time whenthe data transmitted on the transmission resource 620 replaced by aspecific HARQ identifier, e.g. process 4, and the data retransmission isperformed at the timings 660, 665, 670, 675, and 680 corresponding tothe processor 4. In the normal HARQ operation as above, if the HARQ ACKis received, it is determined that the corresponding data is transmittedsuccessfully and notifies the upper layer of the successfultransmission.

FIG. 7 is a diagram illustrating uplink transmission on the time axis inthe LTE system.

Referring to FIG. 7, the uplink transmission of the UE is performed insuch a way that the UE is allocated uplink transmission resource andacquires the size of packet for transmission and MCS information to beapplied. The above information is carried in a control message calleduplink grant which is transmitted in a predetermined format on thephysical channel called PDCCH. The grant message may indicate initialtransmission or adaptive retransmission using a predetermined field. Ifthe grant message for the initial transmission is received in a HARQprocess x at a certain timing as denoted by reference number 705, the UEperforms initial transmission on the transmission resource allocated atthe TTI after 4 TTIs since the TTI at which the uplink grant is receivedas shown in part 710. For example, if the grant message for initialtransmission is received at yth TTI, the initial transmission isperformed at (y+4)th TTI. Afterward, the UE may perform the HARQretransmission of the MAC PDU at every 8th TTI. The HARQ retransmissionis allowed until the CURRENT_TX_NB reaches the maxim number oftransmissions. In an embodiment, the TTIs at which the UE is capable ofperforming HARQ transmission and retransmission for a certain HARQprocess are referred to as transmission occasions. Assuming that themaximum number of transmissions is 4, there are transmission occasions710, 720, 730, and 740 in FIG. 7. If a NACK is received at the previousfeedback occasion or if the grant message indicating adaptiveretransmission at the retransmission grant occasion, the UE performsuplink transmission at the transmission occasion and, otherwise, skipsuplink transmission even at the transmission occasion. The feedbackoccasion is the time after 4 TTIs since the time when the uplinktransmission has been performed. In FIG. 7, time points 715, 725, 735,and 745 may be the feedback occasions or not depending on whether theuplink transmission is performed at the transmission occasion. Theretransmission grant occasions are the time points where the grantmessage indicating adaptive retransmission is supposed to be receivedand TTIs occurring at every 8 TTIs since the initial transmissionbetween the initial transmission grant receipt occasion 705 and the lasttransmission occasion 740. It is noticed that the retransmission grantoccasion and the feedback occasion are identical with each other. Thisis because the feedback occasion occurs after 4 TTI since a certainuplink transmission and the retransmission grant occasion precedes acertain uplink transmission as much as 4 TTIs.

As shown in FIG. 7, upon receipt of the grant message indicating initialtransmission, the UE can determine the transmission occasion andretransmission grant occasion as follows. In the following equation, ydenotes the time point when the grant indicating initial transmission isreceived, and n denotes the maximum number of transmissions.

transmission occasion=(y+4)th TTI,(y+4+1×8)th TTI,(y+4+2×8)th TTI, . . .,(y+4+(n−1)×8)th TTI

retransmission grant occasion=(y+1×8)th TTI,(y+2×8)th TTI, . . .,(y+(n−1)×8)th TTI

The UE increases CURRENT_TX_NB by 1 whenever the transmission occasioncalculated above arrives regardless whether transmission occurs actuallyand monitors the PDCCH at ever retransmission grant occasion to detectreceipt of the grant message indicating adaptive retransmission.

The uplink transmission operation is identical with the semi-persistentresource-based transmission with the except that the uplink grantindicating initial transmission is not received. That is, aftertransmitting the packet on the semi-persistent transmission resource,the UE monitors PDCCH at every retransmission grant occasion until thelast transmission occasion of the packet expires.

Typically, the semi-persistent transmission resource for VoIP occurs atan interval of 20 msec, and the maximum number of transmissions is 5 or6. Although it depends on the channel condition of the UE, it isinefficient to monitor PDCCH at every retransmission grant occasion tothe last transmission occasion in view of battery consumption by takingnotice that the packet is transmitted successfully after 2 or 3transmissions in most cases. Particularly for the battery constrainedUE, the battery lifespan shortage problem caused by unnecessary powerconsumption is more influential than the gain obtained through theadaptive retransmission. In order to solve this problem, the presentinvention proposes a method and apparatus for monitoring PDCCH todetermine whether to restrict or disable or enable the adaptiveretransmission selectively for the UE for which battery saving isimportant, e.g. the UE operating in DRX mode.

For explanation convenience, the terms related to DRX are describedbriefly hereinafter.

Active Time: Time duration in which the UE monitors PDCCH in the DRXmode. The time duration for monitoring PDCCH to receive the adaptiveretransmission grant is included in the active time. In more detail, theactive time is defined as follows. Detailed description thereof isspecified in 36.321.

-   -   At least one of onDurationTimer, drx-InactivityTimer,        drx-RetransmissionTimer, and mac-ContentionResolutionTimer is        running. Hereinafter, referred to as the first type Active Time    -   A scheduling Request is set on PUCCH and is pending.        Hereinafter, referred to as the second type Active Time.    -   An uplink grant for a pending HARQ retransmission can occur and        there is data in the corresponding HARQ buffer. Hereinafter,        referred to as the third type Active Time. If the uplink grant        for the pending HARQ retransmission occurs, this means that the        uplink grant indicating adaptive retransmission occurs.    -   A PDCCH indicating a new transmission addressed to the C-RNTI of        the UE has not been received after successful reception of a        Random Access Response for the preamble not selected by the UE).        Hereinafter, referred to as the fourth type Active Time.

This embodiment relates to a method for saving the battery power of theUE by adjusting the third type Active type. The onDurationTimer,drx-InactivityTimer, and drx-RetransmissionTimer are the timers set bythe eNB to the respective values for the UE to monitor PDCCH when apredetermined condition is fulfilled.

If a subframe is included in at least one of the first to fourth typeactive times, the subframe belongs to the Active Time such that the UEmonitors PDCCH.

Non Active Time: Time duration in which the UE does not monitor PDCCH inDRX mode. This is the sleep time in the entire period with the exceptionof the active time.

Typically, the UE operating in the DRX mode turns off the power to thetransceiver at all times except for the active time so as to minimizepower consumption. In the case of VoIP, the uplink initial transmissionoccurs at every 20 msec and if the UE transitions to the active time ateach retransmission occasion up to the last transmission occasion forreceiving PDCCH, this causes a waste of battery power for receiving theadaptive retransmission grant transmitted at a low incidence frequency.In order to solve this problem, the present invention applies the thirdtype active time selectively according to the instruction of the eNB.

In an embodiment, the eNB sends the UE having a high probability ofsignificant battery consumption by the third type active time such asVoIP a control message instructing to apply the third type active timeselectively. The control message may include DRX-related configurationinformation.

If the DRX starts afterward, the UE determines whether to apply thethird type active time depending on whether the control information isreceived. In more detail, if the control information has not beenreceived, the UE applies the third type active time and, otherwise ifthe control information has been received, applies a modified third typeactive time. The modified third type active time, is the active time inwhich whether to monitor PDCCH in the subframe at which the uplink grantfor pending HARQ retransmission may occur is determined by the HARQprocessor. In more detail, when a subframe is the subframe in whichretransmission uplink grant may occur in corresponding to the HARQprocess having data, if one of the second and third conditions isfulfilled, the active time is not regarded as the third active time(i.e. if the subframe is not other type active time, the UE does notmonitor PDCCH in the subframe).

[Condition 2]

Although the uplink transmission is performed in the HARQ process, noHARQ feedback is received due to the measurement gap. The measurementgap is a time period configured to occur at a predetermined interval inorder for the UE to perform measurement on the serving and otherfrequencies. The UE performs neighbor cell measurement withoutcommunication with the serving cell in the subframe corresponding to themeasurement gap.

If no HARQ feedback is received due to the measurement gap, the UEcannot determine whether to per non-adaptive retransmission. If theuplink transmission is performed ordinarily, the data reception failureprobability is higher than the data reception success probability.Accordingly, if such a situation occurs, the UE operates as if the HARQfeedback of ACK is received. That is, the UE stops non-adaptiveretransmission and resumes the retransmission only when the eNB instructthe adaptive retransmission explicitly. However, the third type ActiveTime is not applied, the UE may not monitor PDCCH to detect the adaptiveretransmission, resulting in failure of correct data transmissionoperation.

In order to solve this problem, the UE determines whether to apply thethird type Active Time by checking whether the condition 2 is fulfilled.

[Condition 3]

The data stored in the corresponding HARQ process is the MAC PDUtransmitted in the random access procedure.

The random access procedure is made up of transmitting at the UE apreamble, transmitting at the eNB a random access response message, andtransmitting at the UE a MAC PDU using the uplink transmission resourceallocated by means of the random access response message. Typically, therandom access procedure is triggered when the data to be transmittedoccurs at the UE, and the UE stores the MAC PDU to be transmitted in apredetermined buffer called a message 3 buffer and if a random accessresponse message is received, transmits the MAC PDU stored in themessage 3 buffer. At this time, the eNB cannot identify the UE whichtransmits the MAC PDU and thus the third type Active Time is applied fornormal operation, i.e. adaptive retransmission, when transmitting theMAC PDU stored in the message 3 buffer.

FIG. 8 is a flowchart illustrating the UE operation according to thesecond embodiment. Referring to FIG. 8, the UE receives variousconfiguration information from the eNB at step 805. The configurationinformation may incudes DRX configuration information, measurement gapconfiguration information, and the first control information indicatingwhether to apply the third type Active Time (or whether to use adaptiveretransmission). The configuration information may be transmitted in onecontrol message or respective control messages. The DRX configurationinformation may include onDurationTimer length, drx-InactivityTimerlength, drx-RetransmissionTimer length, DRX cycle length, and start timeof onDuration. The measurement gap configuration information may includea measurement gap cycle and measurement gap start time. The firstcontrol information may be a 1-bit information indicating whether toapply the third type Active Timer selectively.

The UE performs uplink transmission for a predetermined HARQ process atstep 810 and determines whether to monitor PDCCH in the subframe atwhich an uplink grant indicating adaptive retransmission for the uplinktransmission may be received at step 815.

At step 815, the UE determines whether the DRX is running. If so, theprocedure goes to step 820 and, otherwise, step 825. If the DRX isrunning, this means that the DRX control information (e.g. DRX cycle) isconfigured to the UE.

The UE monitors PDCCH in the corresponding subframe at step 820. IfChannel Quality Indication (CQI) transmission on Physical Uplink ControlChannel (PUCCH) is configured in the subframe, the UE performs CQItransmission on the PUCCH. If SRS transmission is configured in thesubframe, the UE transmits SRS.

The UE determines whether the first control information is configured atstep 825 and, if so, the procedure goes to step 835 and, otherwise, step830. If the first control information is configured, this means that thefirst control information has been received through a predeterminedcontrol message and thus the third type Active Time selectiveapplication operation is configured.

At step 830, if data is stored in the HARQ processor, the UE determinesthat the subframe is the third type Active Time. That is, the UEmonitors PDCCH in the subframe. If no data is stored in the HARQprocess, e.g. if the CURRENT_TX_NB has reached the maximum number oftransmission times and thus the UE has discarded the data stored in thebuffer, the UE assumes that the subframe is the third type active time.That is, the UE does not monitor PDCCH in the subframe. If it isdetermined that the subframe is the third type Active Time or other typeActive Time and if CQI or SRS transmission on PUCCH is configured in thesubframe, the UE performs the corresponding uplink transmission. If thesubframe is neither the third type Active Time nor other type ActiveTime, the UE does not perform any uplink transmission although the CQIor SRS transmission on PUCCH is configured in the subframe.

At step 835, the UE determines whether the HARQ feedback correspondingto the most recent uplink transmission of the HARQ process is receivedcorrectly and whether the mace PDU stored in the HARQ process is the MACPDU acquired from the message 3 buffer. That is, if the reception timeof the HARQ feedback corresponding to the most recent uplinktransmission matches the measurement gap, this means that the HARQfeedback is not received correctly and thus the procedure goes to step830. If the most recent uplink transmission is the MAC PDU transmissionperformed in the random access procedure (i.e. the MAC PDU is of beingacquired from the message 3 buffer), the procedure goes to step 830. Ifthe HARQ feedback is received successfully or if the transmitted MAC PDUis not of being acquired from the message 3 buffer, the UE determineswhether the HARQ feedback is ACK or NACK at step 840. If the HARQfeedback is ACK, the UE assumes that the subframe is not the third typeActive Time at step 845. If the HARQ feedback is NACK, the UE assumesthat the subframe is the third type Active Time.

FIG. 9 is a flowchart illustrating another UE operation according to thesecond embodiment.

FIG. 9 is directed to the method of configuring feedback selectivelydepending on whether the first control information is configured whenthe feedback corresponding to the uplink transmission of the UE is notreceived due to the measurement gap. If the first control information isconfigured (this means that the adaptive retransmission is impossible),the UE assumes the receipt of NACK and, if the first control informationis not received (this means that the adaptive retransmission ispossible), assumes the receipt of ACK so as to delay retransmissionuntil the adaptive retransmission is indicated.

The UE performs uplink transmission for a certain HARQ process at step905. In order to set HARQ_FEEDBACK variable for the HARQ process, theprocedure goes to step 910.

At step 910, the UE determines whether an HARQ feedback is received incorrespondence to the uplink transmission. If the HARQ feedback isreceived, the UE sets the HARQ_FEEDBACK variable according to thereceived HARQ feedback at step 915.

If the HARQ feedback corresponding to the uplink transmission is notreceived for a reason such as measurement gap, the procedure goes tostep 920.

The UE determines whether the first control information is configured atstep 920. If the first control information is configured, this means thefollowings.

-   -   The first control information has not been received and any        control message for releasing the first control information.    -   A function of configuring the third Active Time selectively is        configured.    -   A function of applying HARQ buffer management selectively is        configured (the meaning of applying HARQ buffer management        selectively described later).    -   A function of applying adaptive retransmission selectively is        configured.

If the first control information is configured, the UE sets theHARQ_FEEDBACK to NACK at step 925. That is, the non-adaptiveretransmission is performed at the next retransmission subframe.

If the first control information is not configured, the UE sets theHARQ_FEEDBACK to ACK at step 930. That is, the non-adaptiveretransmission is not performed at the next retransmission subframe.

FIG. 10 is a flowchart illustrating another UE operation according tothe second embodiment.

Referring to FIG. 10, in order to apply adaptive retransmissionselectively depending on whether the first control information isconfigured, if the first control information is configured the UEdiscards the data stored in the HARQ process so as to prevent theadaptive retransmission from occurring in the process.

The UE receives the first control information at step 1005.

The UE receives the HARQ feedback in the uplink HARQ process storingdata currently and selects the process storing the mace PDU which is notbeing acquired from the message 3 buffer among the processes of whichHARQ_FEEDBACK is set to ACK and discards the data stored in the selectedprocess at step 1010. The UE maintains the data stored in the process inwhich the feedback is not received for a reason such as process havingHARQ_FEEDBACK set to NACK and measurement gap.

The UE applies the second HARQ buffer management operation for the nextHARQ operation at step 1-15.

<Second HARQ Buffer Management Operation>

If the received HARQ feedback is NACK and if the CURRENT_TX_NB has notreach the maximum number of transmissions, the UE maintains the datastored in the HARQ buffer.

If the received HARQ feedback is NACK and if the CURRENT_TX_NB hasreached the maximum number of transmissions, the UE discards the datastored in the HARQ buffer.

If the received HARQ feedback is ACK the UE discards the data stored inthe HARQ buffer regardless whether the CURRENT_TX_NB has reached themaximum number of transmissions.

If no HARQ feedback has been received due to the measurement gap and ifthe CURRENT_TX_NB has not reached the maximum number of transmissions,the UE maintains the data stored in the HARQ buffer.

If no HARQ feedback has been received due to the measurement gap and ifthe CURRENT_TX_NB has reached the maximum number of transmissions, theUE discards the data stored in the HARQ buffer.

If the first control information is not configured or if the selectiveapplication of adaptive retransmission is not configured, the UE appliesthe first HARQ buffer management operation.

<First HARQ Buffer Management Operation>

If the CURRENT_TX_NB has not reached the maximum number oftransmissions, UE maintains the data stored in the HARQ buffer and,otherwise the CURRENT_TX_NB has reached the maximum number oftransmissions, discards the data stored in the HARQ buffer, regardlessof the receipt (or not) and the type of the HARQ feedback.

FIG. 16 shows another UE operation.

Step 1606 is identical with step 805.

The UE performs uplink transmission in a predetermined HARQ process atstep 1610, and the procedure goes to step 1615 to perform buffermanagement for the data transmitted in uplink.

At step 1615, the UE determines whether the DRX is running. If so, theprocedure goes to step 1625 and, otherwise, step 1620. If the DRX isrunning, this means that the DRX control information (e.g. DRX cycle) isconfigured to the UE.

At step 1620, the UE applies the third HARQ buffer management operation.

The UE determines whether the first control information is configured tothe UE at step 1625 and, if so, the procedure goes to step 1630 and,otherwise, step 1620.

At step 1630, the UE determines whether the condition 2 or 3 isfulfilled. If at least one of the conditions is fulfilled, the proceduregoes to step 1620 and, otherwise both the conditions are not fulfilled,step 1635 at which the UE applies the fourth HARQ buffer managementoperation.

If the second condition is not fulfilled, this means that the receptiontiming of the HARQ feedback corresponding to the transmitted MAC PDU isnot overlapped with the measurement gap. If the condition 3 is notfulfilled, this means that the transmitted MAC PDU is not the MAC PDUacquired from the message 3 buffer. Accordingly, if the HARQ feedbackreception failure is neither because the transmitted MAC PDU is not theMAC PDU acquired from the message 3 buffer nor because the receptiontiming of the HARQ feedback corresponding to the transmitted MAC PDU isnot overlapped with the measurement gap, the procedure goes to step1635. Otherwise if the transmitted MAC PDU is the MAC PDU acquired fromthe message 3 buffer or the HARQ feedback corresponding to the MAC PDUis not received, the procedure goes to step 1620.

<Third HARQ Buffer Management Operation>

If the CURRENT_TX_NB has not reached the maximum number oftransmissions, the UE maintains the data stored in the HARQ buffer and,otherwise if the CURRENT_TX_NB has reached the maximum number oftransmissions, discards the data stored in the HARQ buffer regardless ofthe receipt or not of the HARQ feedback and type of the HARQ feedback.

<Fourth HARQ buffer management operation>

If the received HARQ feedback is NACK (or HARQ_FEEDBACK is NACK) and ifthe CURRENT_TX_NB has not reached the maximum number of transmissions,the UE maintains the buffer stored in the HARQ buffer.

If the received HARQ feedback is NACK (or HARQ_FEEDBACK is NACK) and ifthe CURRENT_TX_NB has reached the maximum number of transmissions, theUE discards the data stored in the HARQ buffer.

If the received HARQ feedback is ACK (or HARQ_FEEDBACK is ACK), the UEdiscards the data stored in the HARQ buffer regardless whether theCURRENT_TX_NB has reached the maximum number of transmissions or not.

FIG. 35 shows another UE operation.

Step 3505 is identical with step 1605.

The UE in the DRX mode performs uplink transmission of a predeterminedHARQ process and waits for the feedback occasion corresponding to theuplink transmission. If the feedback occasion arrives, the UE receivesthe feedback and determines whether to discard or maintain the data (MACPDU) based on the received feedback at step 3515. If the DRX is running,this means that the DRX control information (e.g. DRX cycle) isconfigured to the UE. If the DRX is not running, the non-use of thethird type Active Time does not contribute to the battery conservation,the UE operates according to the legacy technology.

The UE determines whether the first control information is configured atstep 3515 and, if so, the procedure goes to step 3530 and, otherwise,step 3520.

The UE maintains the data stored in the buffer regardless of the type ofthe received feedback at step 3520. The data is discarded when apredetermined condition is fulfilled afterward.

The UE determines whether the condition 3 is fulfilled at step 3530.That is, the UE determines whether the transmitted MAC PDU is the MACPDU acquired from the message 3 buffer. If the transmitted MAC PDU isacquired from the message 3 buffer, this means that the UE is in therandom access procedure and the eNB may not identify the UE correctlyyet. Accordingly, it is necessary to make in possible to performadaptive retransmission by applying the third type Active Time. If thetransmitted MAC PDU is not acquired from the message 3 buffer and if apredetermined condition is fulfilled, the procedure goes to step 3535 soas not to apply the third type Active Time.

The UE determines whether the received feedback is HARQ ACK or NACK atstep 3535. If the HARQ feedback is NACK, this means that thenon-adaptive retransmission is commanded and thus the UE maintains theMAC PDU stored in the buffer for use in the non-adaptive retransmissionat step 3520. If the HARQ feedback is ACK, the procedure goes to step3540.

The UE determines whether the current operation mode is FDD or TDD atstep 3540. If the current operation mode is FDD, this means that thefeedback occasion and retransmission grant occasion is the same subframeand thus the procedure goes to step 3545.

The UE determines whether the PDCCH indicating retransmission isreceived in the corresponding subframe at step 3545. The UE maydetermine whether only the feedback is received but not the PDCCHindicating retransmission. If the PDCCH indicating the retransmission isreceived, the procedure goes to step 3520. If only the ACK is receivedbut the PDCCH indicating retransmission is not received, the UE discardsthe data stored in the buffer at step 3550.

The UE maintains the data stored in the buffer before the retransmissiongrant occasion arrives at step 3555. If the retransmission grantoccasion arrives, the UE determines whether the PDCCH indicatingadaptive retransmission at step 3560. If the PDCCH is received, theprocedure goes to step 3520 and, otherwise, step 3550. In the TDD mode,the retransmission grant occasion and the feedback occasion are definedaccording to the TDD configuration as specified in TS 36.213.

Third Embodiment

In order to increase the data rate of the UE, a technique called carrieraggregation for aggregating multiple serving cells for one UE isintroduced.

FIG. 11 is a diagram illustrating the carrier aggregation.

Referring to FIG. 11, an eNB transmits and receives multiple carriersacross several frequency bands in general. For example, in the case thatthe eNB 105 transmit the carrier 1115 having the downlink centerfrequency f1 and the carrier 1110 having the downlink center frequencyf3, If the carrier aggregation is not supported as in the conventionaltechnology, the UE has to transmit/receive data using one of the twocarriers. However, the eNB can allocate more carriers to the UE 1130having the carrier aggregation capability depending on the situation soas to increase the data rate of the UE 1130. The technique ofaggregating the downlink carriers or uplink carriers as described aboveis referred to as carrier aggregation.

The terms to be used in the following embodiments are described herein.

Assuming that a cell is configured with one downlink carrier and oneuplink carrier in the conventional concept, the carrier aggregation canbe understood as if the UE communicates data via multiple cells. Withthe use of carrier aggregation, the peak data rate increases inproportion to the number of aggregated carriers.

In the following description, the phrase “a UE receives data through acertain downlink carrier or transmits data through a certain uplinkcarrier” means to receive or transmit data through control and datachannels provided in cells corresponding to center frequencies andfrequency bands characterizing the carriers. In the present invention,carrier aggregation may be expressed like that a plurality of servingcells are configured with the terms such as primary serving cell(PCell), secondary serving cell (SCell), and activated serving cell.These terms are used in the same meanings as used in the LTE mobilecommunication system as specified in TS 36.321.

When an SCell is configured or activated to the UE or when the SCell isreleased or deactivated, the UE may reconfigure the Radio FrequencyFrontend. This includes reconfiguring a filter bandwidth of the RadioFrequency Frontend according to the situation of reconfiguration orreactivation or release or deactivation, and the datatransmission/reception is suspended while the UE performsreconfiguration. Assuming that the time period for suspending datatransmission/reception is time period 1, if the time period 1 occursfrequently, this may cause performance degradation.

The Radio Frequency Frontend reconfiguration is characterized byfollowing features.

-   -   The time period 1 occurs in the serving cell having the same        frequency band as the SCell being newly configured or released        or activated or deactivated.    -   The length of the time period 1 may change depending on the        hardware performance as UE processing capability.    -   If the Radio Frequency Frontend is not reconfigured, the power        consumption of the UE increases as compared to the case of        reconfiguring the Radio Frequency Frontend. The Radio Frequency        Frontend reconfiguration is not a mandatory operation but has a        tradeoff relationship between the power consumption of the UE        and the performance degradation.    -   If it is determined to perform Radio Frequency Frontend        reconfiguration and if the serving cells x and y are configured        on certain frequency bands, the Radio Frequency Frontend        reconfiguration is required before or after the measurement of        neighbor cells of the serving cell x or y.    -   If it is determined to reconfigure the Radio Frequency Frontend,        the Radio Frequency Frontend reconfiguration is required when        the state of the serving cell x transitions from the activated        state to the deactivated state or from the deactivated state to        the activated state.    -   Accordingly, the shorter the neighbor cell measurement cycle is        and the more frequently the activation/deactivation occurs, the        more significant the performance degradation caused by the Radio        Frequency Frontend reconfiguration becomes.

By taking notice of the above characteristics, the present inventionproposes the following operation.

-   -   The UE reports the Radio Frequency Frontend reconfiguration        necessity per frequency band combination it supports to the eNB.    -   The eNB informs the UE of the Radio Frequency Frontend        reconfiguration scheme in configuring at least one SCell to the        UE. If it is likely to command activation and deactivation of        the SCell or neighbor cell measurement for the SCell frequently,        the eNB instructs to apply the Radio Frequency Frontend        reconfiguration operation 1 and, otherwise, Radio Frequency        Frontend reconfiguration operation 2.

FIG. 12 is a flowchart illustrating the UE operation according to thethird embodiment.

Referring to FIG. 12, the UE reports its capability to the eNB at step1205. At this time, the UE reports the frequency bands it supports andfrequency band combinations for carrier aggregation and, if thefrequency band combination is inter-band combination, reports the RadioFrequency Frontend reconfiguration necessity. For example, the UE maysupport the frequency bands x and y and carrier aggregation as follows.

TABLE 1 Radio Frequency Frontend reconfiguration necessity Bandcombination report Frequency band 1 serving cell on band x NOcombination 1 Frequency band 1 serving cell on band y NO combination 2Frequency band 2 serving cells on band x YES combination 3 Frequencyband 2 serving cells on band y YES combination 4 Frequency band 1serving cell on band x, NO combination 5 1 serving cell on band yFrequency band 2 serving cells on band x, YES combination 6 1 servingcell on band y

The UE includes the 1-bit information for reporting the Radio FrequencyFrontend reconfiguration necessity to the frequency band fulfilling thefollowing condition.

Band combination of configuring at least two serving cell on one band.

Since two serving cells are configured on the band x in the frequencyband combination 3 in the above example, the UE reports the RadioFrequency Frontend reconfiguration necessity. Since two serving cellsare configured on the band x in the frequency band combination 6 too,the UE reports the Radio Frequency Frontend reconfiguration necessity.

The UE receives a control message for configuring at least one SCell atstep 1210. The UE determines whether the frequency of the SCell isneighboring to the frequency of the serving cell configured already inthe same frequency band at step 1215. If this condition is notfulfilled, the UE does not perform the Radio Frequency Frontendreconfiguration at step 1220. If the condition is fulfilled, theprocedure goes to step 1225.

At step 1225, the UE determines whether the measure cycle to be appliedto the SCell in the deactivated state is greater than a threshold atstep 1225. The measurement cycle may be configured per frequency and isa value indicating the measurement cycle to be applied when an SCell isconfigured and in the deactivated state on the frequency whileconfiguring measurement on a certain frequency using a predeterminedcontrol unit and when the UE measures the channel state of the SCell.The threshold may be configured by the eNB using a predetermined controlmessage or fixed to a value. If the measurement cycle is equal to orless than the threshold, the procedure goes to step 1230 and otherwise,step 1235.

If the procedure goes to step 1230, this means that the Radio FrequencyFrontend reconfiguration occurs frequently and thus the UE reconfigurethe Radio Frequency Frontend with the inclusion of the newly configuredSCell. Afterward, the UE maintains the reconfigured Radio FrequencyFrontend in the SCell deactivation state regardless of the measurement.For example, when the frequency of the newly configured SCell is f1 andthe frequency of the serving cell configured already on the samefrequency band is f2, if a control message for configuring an SCell isreceived, the UE reconfigures the Radio Frequency Frontend to includeboth the f1 and f2 and maintains the reconfigured Radio FrequencyFrontend until the SCell is released. When the SCell is newly configuredin this way, reconfiguring the radio Frequency Frontend to include thefrequency of the configured SCell immediately and maintaining theconfiguration until the SCell is released is referred to as RadioFrequency Frontend reconfiguration scheme 1.

At step 1235, the UE determines whether the control message includes thecontrol information instructing to apply the Radio Frequency Frontendreconfiguration method 2. If this control information is not included,the procedure goes to step 1230 and otherwise if the control informationis included, step 1240.

If the procedure goes to step 1240, this means that the measurementcycle is greater than the threshold (i.e., UE does not need to measurefor reconfiguration frequently) and the eNB does not perform SCellactivation/deactivation frequency of the eNB frequently and thus the UEapplies the Radio Frequency Frontend reconfiguration scheme 2 which isperformed at the time when the Radio Frequency Frontend reconfigured isnecessary. That is, when the SCell is not activated and there is no needof performing the SCell measurement, if it becomes necessary toconfigure the radio Frequency Frontend to include f2 and perform themeasurement in spite of the deactivated state of the SCell or if theSCell is activated, the UE reconfigure the Radio Frequency Frontend toinclude both the f1 and f2.

In the present invention, the reconfiguration scheme 2 indicator may besimplified in association with the measurement cycle. For example, ifthe measurement cycle to be applied to the deactivated SCell is greaterthan the threshold, it is assumed that the reconfiguration scheme 2 isindicated and, otherwise if the measurement cycle is equal to or lessthan the threshold, it is assumed that the reconfiguration scheme 2 isnot indicated. In this case, when a serving cell which operates on thesame frequency band of the previously configured serving cell (e.g.,PCell) and which has the frequency neighboring the frequency ofpreviously configured serving cell is configured, if the measurementcycle to be applied when the serving cell to be configured is in thedeactivated state is greater than the threshold, the UE applies theRadio Frequency Frontend reconfiguration scheme 2 and, otherwise themeasurement cycle is equal to or less than the threshold, applies theRadio Frequency Frontend reconfiguration scheme 1. That is, step 1335 isskipped and, if the condition of step 1330 is fulfilled, the procedurejumps to step 1340.

In summary, the UE selects the Radio Frequency Frontend reconfigurationscheme by taking notice of the following.

-   -   When an SCell is configured and a serving cell (e.g. PCell)        which is in the activated state and operating on the neighboring        frequency in the same frequency band as the SCell;    -   If the measurement cycle to be applied to the deactivated SCell        is greater than a predetermined threshold, the UE has not to        generate any interruption in the serving cell in the activated        state when configuring or releasing the SCell and may generate        interruption in the serving cell in the activated state when the        SCell is activated or deactivated or when the SCell has to be        measured in the deactivated state (i.e., the Radio Frequency        Frontend reconfiguration scheme 2 has to be applied).    -   If the measurement cycle to be applied to the SCell in the        deactivated state is equal to or less than the threshold, the UE        may generate interruption in the serving cell in the activated        state when configuring or releasing the SCell but has not to        generate interruption to the serving cell in the activated state        when the SCell is activated or deactivated or the SCell has to        be measured in the deactivated state (i.e., Radio Frequency        Frontend reconfiguration scheme 1 has to be applied).

When reconfiguring the Radio Frequency Frontend, an interruption may begenerated to the serving cell (e.g., PCell) in the activated state. Indetail, the UE may not receive or transmit the following signals.

-   -   HARQ feedback signal corresponding to PUSCH transmitted through        PCell    -   PUSCH transmission through PCell    -   CSI signal transmission through PCell    -   D-SR signal transmission through PCell    -   Preamble signal transmission through PCell    -   RAR signal transmission through PCell

The interruption according to the Radio Frequency Frontendreconfiguration may be classified into two types:

Interruption 1: The UE determines the time period in which theinterruption caused by the Radio Frequency Frontend reconfiguration isgenerated. The eNB knows the occurrence of interruption but not theinterruption occurrence time.

Interruption 2: The time period when the interruption caused by theRadio Frequency Frontend reconfiguration occurs is predetermined. TheeNB may schedule the UE outside the time period in which theinterruption is generated.

The Radio Frequency Frontend reconfiguration may be classified intothree types:

When the UE configures or releases an SCell in the same frequency bandas the PCell

When the UE performs measurement to the SCell in the deactivated statein the same frequency band as the PCell

When the UE activates or deactivates an SCell in the same frequency bandas the PCell

Among the above cases, the second case generates interruption 1 alwaysbecause the UE determines the measurement timing by itself.

In the first and third cases, the UE performs a predetermined operationaccording to the command of the eNB such that interruption 2 is generatewhen the UE configures the Radio Frequency Frontend in a predeterminedtime period, e.g. a predetermined length of period after a predeterminedtime lapses since the time indicated by the eNB. Even in the first andthird cases, however, the UE may have the right to generate theinterruption 1. Particularly when an SCell is deactivated due to theexpiry of the SCell deactivation timer, the eNB cannot specific theexpiry time and thus interruption 1 is generated always.

The UE manages variables as follows to establish synchronization withthe eNB for the transmission-related information in performing PUSCHtransmission.

-   -   HARQ_FEEDBACK: Variable storing HARQ feedback corresponding to        PUSCH transmission. If HARQ_FEEDBACK is NACK, retransmission is        performed at the next transmission occasion and, otherwise if        the HARQ_FEEDBACK is ACK, retransmission is not performed.    -   CURRENT_TX_NB: Variable storing a number of PUCCH transmissions        of the packet to which current HARQ operation is applied. If the        CURRENT_TX_NB reaches a predetermined threshold, the UE discards        the corresponding packet stored in the buffer.    -   CURRENT_IRV: Variable storing Redundancy Version (RV) to be        applied to the packet to which current HARQ operation is        applied. The UE applies the RV indicated by the CURRENT_IRV when        transmitting PUSCH.

These variables are updated whenever the UE receives HARQ_FEEDBACK ortransmits PUSCH. If the eNB know that the PUSCH transmission is notoccurred, it is preferred for the UE and the eNB to maintain theCURRENT_IRV as it is. the uplink HARQ operation is defined to apply aspecific RV automatically whenever the non-adaptive retransmission(retransmission performed with the transmission resource which the UEhas used at the previous transmission, and the UE performs thenon-adaptive retransmission basically upon receipt of NACK as feedback)is performed. For example, the UE applies RV 0 to the initialtransmission, RV 2 to the first non-adaptive retransmission, RV 3 to thesecond non-adaptive retransmission, and RV 3 for the third non-adaptiveretransmission. The UE and the eNB determine the RV to be applied to thenext retransmission using CURRENT RV. If the CURRENT_IRV increases eventhough PUSCH transmission is not performed, the transmission isperformed with missing out part of RV, resulting in performancedegradation. Accordingly, when the eNB knows that the UE has nottransmitted PUSCH, it is preferred to maintain the CURRENT_IRV as it iswithout increment.

Otherwise if the eNB does not know that the UE has not transmittedPUSCH, it is much important for the UE and the eNB to perform encodingand decoding with the same RV by increasing the CURRENT_IRV.Accordingly, if the PUSCH transmission is omitted by the interruption 1,it is preferred to maintain the CURRENT_IRV and, otherwise if the PUSCHtransmission is omitted by the interruption 2, it is preferred toincrease the CURRENT_IRV. Or by taking notice that the occurrencefrequency of the interruption 2 is higher than that of the interruption1, it is possible to discard the data instead of increasing theCURRENT_IRV so as to prevent retransmission from occurring.

The CURRENT_TX_NB is used to prevent retransmission from occurring whenthe transmission fails even it has been performed over a predeterminednumber of transmissions. If the number of transmissions of the currentpackets reaches a predetermined threshold, the UE discards the packetstored in the HARQ buffer and does not perform retransmission any more.If the number of transmission of the current packet reaches thepredetermined threshold, the eNB assumes that there is no morenon-adaptive retransmission of the packet and then allocates thefrequency/time transmission resource, which has been allocated for thepacket transmission, to another UE. Accordingly, it is important for theUE and the eNB to determine that the number of transmissions of thecurrent packet reaches the threshold at the same timing and, in order toaccomplish this, the UE and the eNB manage the CURRENT_TX_NB based onthe number of retransmission occasions expired other than the number ofactual PUSCH transmissions. That is, the UE and the eNB increment theCURRENT_TX_NB by 1 whenever the transmission occasion of a certainpacket expires although no packet is transmitted actually. Accordingly,the UE increments the CURRENT_TX_NB by 1 in any case that the eNB knowsor not that the UE has not transmitted PUSCH. Thus, either theinterruption 1 or the interruption 2 increments the CURRENT_TX_NB by 1.

FIG. 36 proposes a method of adjusting the variables related to theuplink transmission at the UE.

An interruption occurs due to the Radio Frequency Frontendreconfiguration fulfilling a predetermined condition at step 3605. TheUE determines whether to receive PHICH in a subframe in the course ofthe occurrence of the interruption at step 3610. For example, when asubframe sf [m] belongs to the interruption time period, if PUSCH istransmitted at sf [m−4] in the PCell, it is necessary to receive PHICHat sf [m], and thus the procedure goes to step 3615. If it is notnecessary to receive PHICH, the procedure goes to step 3620. The RadioFrequency Frontend reconfiguration fulfilling the predeterminedcondition means the Radio Frequency Frontend reconfiguration generatinginterruption in the PCell.

Although no HARQ feedback is received, the UE sets the relatedHARQ_FEEDBACK to ACK at step 3615. This is the case that the UE hastransmitted PUSCH but has not receive the feedback corresponding theretoand thus sets the feedback to ACK to prevent non-adaptive retransmissionfrom occurring.

The UE determines whether to transmit PUSCH in the interruptionoccurrence period at step 3620. For example, when sf [n] belongs to theinterruption occurrence period, if the PDCCH indicating retransmissionor initial transmission or HARQ feedback set to NACK is received at sf[n−4], the UE has to transmit PUSCH at sf [n].

If it is not necessary to transmit PUSCH, the procedure ends at step3625. If it is necessary to transmit PUSCH, the UE determines whetherthe interruption is interruption 1 or interruption 2 and, if theinterruption is interruption 1, the procedure goes to step 3640 and,otherwise if the interruption is interruption 2, step 3635. For example,the Radio Frequency Frontend reconfiguration triggered the interruptionrelates to the measurement to the SCell in the deactivated state on thesame frequency band as the PCell, the procedure goes to step 3635 and,otherwise if the Radio Frequency Frontend reconfiguration triggered theinterruption relates to the activation of the SCell in the deactivatedstate on the same frequency band as the PCell, step 3640. At step 3635,the UE increments the CURRENT_TX_NB related to the PUSCH transmission by1 and maintains the CURRENT_IRV as it is. Then the procedure ends.

At step 3640, the UE maintains the CURRENT_TX_NB and the CURRENT_IRVrelated to the PUSCH transmission as they are. Or the UE discards thedata stored in the HARQ buffer for PUSCH transmission and initializesthe variables.

The SCell deactivation is performed when the MAC control informationindicating SCell deactivation or the SCell deactivation timer expires.In the former case, the eNB instructs the deactivation of the SCell, andthe UE reconfigure the Radio Frequency Frontend in a predetermined timeperiod such that the PCell interruption occurs in a predicted timeperiod. In the latter case, the UE deactivates the SCell without eNB'sawareness such that the eNB does not predict the interruption occurrenceperiod. For reference, the deactivation timer is managed per SCell and,if the UE does not receive scheduling in the corresponding SCell beforeexpiry of the deactivation timer, the UE deactivates the correspondingSCell by itself. This is to prevent the activated state from beingmaintained erroneously when the MAC control signal indicatingdeactivation is lost.

The UE operation related to the deactivation of the SCell configured onthe same frequency band as the PCell is depicted in FIG. 37.

An SCell is deactivated at step 3705.

The UE determines whether the SCell is deactivated due to the receipt ofa MAC control information indicating deactivation or the expiry of thedeactivation timer at step 3710. If the SCell is deactivated due to thereceipt of the MAC control information, the procedure goes to step 3715.At step 3715, the UE performs Radio Frequency Frontend reconfigurationin a predetermined time period such that the PCell interruption isgenerated in a predictable time period. The predictable time period maybe defined based on the period in which the MAC control informationindicating deactivation is received. For example, if the MAC controlinformation is received a sf [n], the time duration may be sf[n+9]˜sf[n+5].

If it is necessary to transmit PUSCH of the PCell in the interruptionoccurrence period, the UE increment the related CURRENT_TX_NB by 1 andmaintains the CURRENT_IRV as it is at step 3720.

If the SCell is deactivated due to the expiry of the deactivation timer,the procedure goes to step 3725. At step 3725, the UE selects the timeperiod fulfilling the following conditions as many as possible andperforms the Radio Frequency Frontend reconfiguration to generate thePCell interruption in the corresponding time period.

[PCell Interruption Occurrence Period Selection Condition]

Time duration in which the following signals are not transmitted andreceived through the PCell. Or time period in which transmission andreception are least. Priorities may be applied in the order asenumerated herein.

-   -   PCell preamble transmission    -   PUCCH transmission    -   PCell PHICH reception    -   PCell PUSCH transmission    -   PCell SRS transmission

For example, if the PCell SRS is transmitted in time period 1 and thePUCCH is transmitted in time period 2, the UE selects the time period 1with priority.

Next, the UE performs Radio Frequency Frontend reconfiguration togenerate the PCell interruption in the selected time period.

If the PCell PUSCH should have to be performed in the selected timeperiod, the UE increment both the related CURRENT_TX_NB and CURRENT_IRVby 1 at step 3730.

The above operation may be generalized for all pc interruptions. Forexample, if the PCell interruption is generated, the UE determineswhether the interruption is interruption 1 or interruption 2 and, if theinterruption is interruption 1, performs steps 3725 and 3730 and,otherwise if the interruption is interruption 2, steps 3715 and 3720.

Fourth Embodiment

When a plurality of serving cells are configured to a UE, TAG is usedfor managing the uplink transmission timings of the serving cellsefficiently. The TAG includes at last one serving cell, and at least oneTAG is configured to one UE. The serving cells belonging to a TAG sharethe same uplink transmission timing. The TAG including the PCell isreferred to as P-TAG, and the TAG consisting of SCells is referred to asS-TAG.

The eNB has to configure the TAG to the UE appropriately inconsideration of the UE location, and it may be necessary to reconfigurethe current TAG of the UE as the UE moves. If a serving cell belongingto a TAG moves to another TAG, the UE has to change the uplinktransmission timing of the serving cell in adaptation to the new TAG. Atthis time, changing the transmission timing abruptly is neither possiblenor preferable. The eNB and the UE stop downlink/uplink transmission inthe serving cell and, when the reconfiguration occurs, deactivate theserving cell implicitly to change the transmission timing gradually.

FIG. 13 is a flowchart illustrating the UE operation according to thefourth embodiment.

Referring to FIG. 13, if the UE receives a control message forconfiguring SCell and TAG from the eNB at step 1305, the procedure goesto step 1310.

At step 1310, the UE determines whether the control message is theinitial control message including the TAG configuration information.That is, no TAG is configured to the UE explicitly before receiving thecontrol message, and the UE determines whether all the serving cellsshare the same uplink transmission timing. If this condition isfulfilled, the UE configures all of the servings configured previouslyinto P-TAG at step 1315. Then the UE performs steps 1320 to 1350 perSCell to be configured newly or for which TAG information is indicatedto determine the TAG to which the corresponding SCell belongs for theSCells to be configured newly.

The UE selects the SCell to which the TAG configuration operation is notperformed among the SCells and determines whether the control messageincludes the TAG information for the SCell explicitly at step 1320 and,if so, the procedure goes to step 1325 and, otherwise, step 1340.

The UE adds the SCell to the TAG indicated by the TAG information (i.e.sets the uplink transmission timing of the SCell to the same value asthe other SCells of the TAG) at step 1325, and then the procedure goesto step 1330.

At step 1330, the UE determines whether any TAG information differentfrom the current TAG information has been configured for the SCell. Ifnot so, the UE performs the TAG configuration operation for the nextSCell at step 1320. If any TAG information different from the currentTAG information has been configured, this means that the TAG of theSCell is changed from on TAG to another, and the procedure goes to step1335. At step 1335, the UE does not perform uplink transmission in theSCell until the uplink transmission timing is adjusted. Particularly,the UE mutes the periodic uplink signal such as Sounding ReferenceSignal (SRS). In order to accomplish this, the UE deactivates the SCellby itself. For example, the UE may stop or terminate the deactivationtimer of the SCell. The deactivation timer is the timer managed perSCell and restarts whenever scheduling per SCell occurs and, if thetimer expires, the UE deactivates the SCell.

The UE adjusts the uplink transmission timing of the SCell in match withthe new TAG and then returns the procedure to step 1320.

At step 1340, the UE determines whether the TAG information has beenconfigured for the SCell previously. That is, the UE determines whetherthe SCell belongs to a TAG. If so, the procedure goes to step 1345 and,otherwise, step 1350.

At step 1345, the UE determines to maintain the TAG of the correspondingSCell and returns the procedure to step 1320.

At step 1350, the UE adds the corresponding SCell to the P-TAG andreturns the procedure to step 1320.

Fifth Embodiment

As described above, the PDCP layer processes the data from the upperlayer and transfers the processed data to the RLC layer and processesthe data from the RLC and transfers the processed data to the upperlayer. The PDCP layer is responsible for ciphering data from the upperlayer and deciphering the data from the RLC layer. The UE ciphers theupper layer data at an appropriate time and generates PDCP PDU to theRLC layer at the time when the uplink transmission resource isavailable. The PDCP layer stores the PDCP packet (PDCP PDU or PDCP SDU)until the RLC layer checks that corresponding data is transmittedsuccessfully. If a timer pertaining to the PDCP packet (hereinafter,referred to as timer 1) expires, the PDCP packet is discarded eventhough the successful transmission is not confirmed by the RLC layer.The timer 1 starts at the time when a PDCP packet arrives at the PDCPlayer and the length of the timer is set by the network.

The PDCP reception entity performs deciphering using the PDCP sequencenumber (PDCP SN) of the received PDCP PDU as follows.

1. COUNT determination. The COUNT is a 32-bit integer incrementing by 1at every packet. The LSBs of COUNT are PDCP SN, and the rest MSBs areHyper Frame Number (HFN). The length of the HFN varies depending on thelength of the PDCP SN. For example, if the PDCP SN is 12 bits, the HFNis 20 bits; and if the PDCP SN is 15 bits, then the HFN is 17 bits. ThePDCP device maintains and manages the variables related to the PDCP SN(Next_PDCP_RX_SN; value obtained by adding 1 to the highest PDCP SNamong the received SNs) and which received most recently (or havinghighest SN or expected to be received next) and the variables (RX HFN)related the HFN in use currently. If a PDCP PDU is received, the PDCPlayer compares the SN of the PDCP PDU with Next_PDCP_RX_SN to determinewhether to increment HFN. For example, as the comparison result, if itis determined that the received PDCP SN is wraparound (i.e. SN reachesthe maximum value and then returns to 0 to increase again), the PDCPlayer increments HFN by 1 and, otherwise, maintains the HFN. In order todetermine whether the SN is wraparound, the PDCP layer usesReordering_Window. The Reordering_Window has a size as long as half thenumber of sequence numbers indicated by the PDCP SN. For example, if thePDCP SN is 12 bits, the Reordering_Window size is 2048 as half of 4096and, if the PDCP SN is 15 bits, 16384 as half of 32768. The UEdetermines whether the difference between the received PDCP SN andNext_PDCP_RX_SN is greater than the size of the Reordering_Window todetermine whether to increment HFN.

2. The UE deciphers the received PDCP PDU by applying the determinedCOUNT and using a predetermined key.

If handover occurs, retransmission of the missing PDCP packet may berequested. After inter-eNB handover is performed, the UE and the eNBprotect against data loss by exchanging PDCP STATUS REPORT. In theexample of downlink transmission, the source eNB 1715 sends the UE 1705a HANDOVER COMMAND message at step 1720 and forwards the PDCP SDUs ofwhich successful transmission is not confirmed to the target eNB 1710 atstep 1725. After being handed over to the target eNB, the UE sends thetarget eNB a HANDOVER COMPLETE message to notify that the handover issuccessful at step 1730. If the target eNB allocates uplink transmissionresource to the UE at step 1735, the UE sends the target eNB a PDCPSTATUS REPORT including downlink PDCP SDU reception status at step 1740.The target eNB performs downlink data transmission starting from themissing PDCP SDUs by referencing the PDCP STATUS REPORT at step 1745.

At this time, if the difference between the SN of the missing PDCP SDUto be retransmitted and the Next_PDCP_RX_SN of the UE is equal to orgreater than the Reordering_Window, the UE regards the missing PDCP SDUas a new PDCP SDU so as to increment HFN by 1 erroneously. For example,the UE requests for retransmission of the PDCP SN 10 using the PDCPSTATUS REPORT and, at this time, the Next_PDCP_RX_SN is 3000. If the eNBretransmits the PDCP SN 10, the distance between 10 and 3000 is greaterthan the Reordering_Window and thus the UE misunderstands the SN 10 aswraparound sequence number.

The above problem occurs because the difference between the sequencenumber of the PDCP PDU and the Next_PDCP_RX_SN of the PDCP receptionentity is greater than the Reordering_Window size. Accordingly, the bestsolution is to prevent the PDCP transmission entity from causing theabove problem. However, the PDCP transmission entity cannot adjust theNext_PDCP_RX_SN, this solution is not applicable. The present inventionproposes the following solution.

-   -   The PDCP transmission entity manages the sequence number of the        packet to be transmitted next with a variable called        Next_PDCP_TX_SN.    -   The PDCP transmission entity transmits a new packet to update        Next_PDCP_TX_SN only when the difference between the        Next_PDCP_TX_SN and a predetermined sequence number x is not        greater than the Reordering_Window.    -   The X is the lowest sequence number among the sequence numbers        of the PDCP packets that are transmitted but successful        transmission thereof are not confirmed by the RLC layer (or the        sequence number of the PDCP packet arrived first at the PDCP        buffer among the PDCP packets that are stored in the current        PDCP buffer but not transferred to the lower layer).

Since the Next_PDCP_TX_SN is equal to or greater than theNext_PDCP_RX_SN always, it is possible to prevent the PDCP receptionentity to requesting for retransmission of the PDCP packet of whichsequence number is less than the Next_PDCP_RX_SN as much asReordering_Window by controlling such that the packet of which sequencenumber is greater than the least sequence number X among the PDCPpackets which is likely to be retransmitted (i.e. PDCP packetstransmitted already but successful transmission thereof is not confirmedby the RLC layer) as much as Reordering_Window (i.e. the Next_PDCP_TX_SNdoes not exceed the X+Reordering_Window).

The operation of the PDCP entity is depicted in FIG. 18.

A request for transferring data to the lower layer is made to a PDCPentity at step 1805. For example, if the UE is allocated uplinktransmission resource, the MAC layer selects a PDCP entity to transmitdata according to an predetermined criterion and requests the selectedPDCP entity to generate a PDCP PDU.

The PDCP entity determines whether the RLC entity connected thereto isan RLC Acknowledged Mode (AM) entity at step 1810. The RLC entity mayoperate in one of AM, Unacknowledged Mode (UM), and Transparent Mode(TM) and, the retransmission of the PDCP layer occurs only when the RLCentity is the RLC AM entity, i.e., when the PDCP entity belongs to theRLC AM bearer. If the RLC bearer is the RLC AM bearer, the proceduregoes to step 1815 and, otherwise, step 1820. At step 1815, the PDCPentity determines whether statusReportRequired is configured. It is notnecessary to apply the retransmission of the PDCP layer to all RLC AMbearers. In order to apply the PDCP layer retransmission operation forRLC AM bearer selectively per bearer, the eNB configures whether toperform the PDCP retransmission operation (operation in which the PDCPreception entity generates the PDCP status report and the PDCPtransmission entity retransmits the missing PDCP PDU) to the UE usingthe parameter per RLC AM bearer. If the parameter is set to ‘YES,’ thismeans that there is HFN error probability due to the PDCP retransmissionafterward and thus the procedure goes to step 1825. If the parameter isset to ‘NO,’ there is no probability of error caused by PDCPretransmission and thus the procedure goes to step 1820.

At step 1820, the UE generates PDCP PDUs as many as necessary to thelower layer independently of the distance between X and Next_PDCP_TX_SN.Whenever the PDCP PDU is transferred to the lower layer, the UE updatesthe Next_PDCP_TX_SN by referencing the sequence number of thecorresponding PDCP PDU.

At step 1825, the UE generates the PDCP PDUs to the lower layer in therange that the distance between the Next_PDCP_TX_SN and X does notexceed the size of Reordering_Window. That is, the UE generates PDCPPDUs to the lower layer such that the COUNT value corresponding to(X+Reordering_Window) does not becomes greater than the COUNT valuecorresponding to the Next_PDCP_TX_SN.

The HFN error also may occur when the number of PDCP PDUs to bediscarded due to the expiry of the timer 1 is greater than theReordering_Window. Typically, upon receipt of a packet from the upperlayer, the UE ciphers the packet immediately to generate and store aPDCP buffer. If the lower layer requests for data transfers afterward,the PDCP layer transfers the PDCP PDU generated in advance to the lowerlayer. The reason for deciphering the data in advance is because thedeciphering is a very complex operation and thus it may be difficult tocontinue deciphering especially when the data is transmitted at a highdata rate.

If the PDU is not transferred to the low layer until the timer 1 expiresafter the PDCP PDU is generated, the PDU is discarded. If the number ofPDUs discarded consecutively without being transferred to the lowerlayer is greater than a predetermined threshold (e.g.Reordering_Window), FHN error may occur.

An operation for solving the above problem is depicted in FIG. 19.

If a packet arrives from the upper layer at step 1905, the UE startstimer 1 for the corresponding packet, and the procedure goes to step1910. At step 1910, the UE assigns a PDCP SN to the packet and checksthe PDCP condition 1 to determine whether to cipher the packet at step.If the PDCP condition 1 is fulfilled, the procedure goes to step 1915and, otherwise, step 1920. The PDCP condition 1 is of determining theHFN error probability when the sequence number is assigned immediatelyas follows.

[PDCP Condition 1]

The number of the first type PDCP PDUs is greater than threshold 1.

The first type PDCP PDU is the PDCP PDU which has been assigned asequence number and ciphered but not transferred to the lower layer(i.e. not transmitted). Since the first type PDCP PDU may become thesecond type PDCP PDU potentially, whether to assign the PDCP sequencenumber is determined based on the number of the first type PDCP PDUs.The second type PDCP PDU is the PDCP PDU discarded due to the expiry ofthe first timer among the PDCP PDUs that have been assigned sequencenumbers and ciphered but not transferred to the lower layer. Thethreshold 1 is set to an appropriate value based on theReordering_Window size, recent radio channel status, data rate, and UEprocessing capability. For example, if the UE has a high processingcapability, the necessity of ciphering in advance decreases and thus thethreshold 1 may be set to a low value. If the channel condition is goodand the data rate is high, the threshold 1 may be set to a high value.The maximum value of the threshold 1 cannot exceed the Reordering_Windowsize.

[Another PDCP Condition 1]

The number of the second type PDCP PDUs is greater than threshold 2.

It is also preferred to set the threshold 2 to a value based on theReordering_Window size, recent radio channel status, data rate, and UEprocessing capability but less than threshold 1.

The UE generates a PDCP PDU by assigning a sequence number to the packetand ciphering the packet and stores the PDCP packet in the PDCP bufferat step 1920. Next, the UE waits for a new packet.

The UE waits without assigning any PDCP SN to the packet at step 1915.

Next, the UE determines whether the PDCP condition 2 is fulfilled atstep 1925. The PDCP condition 2 is of determining whether the UE resumesthe ‘immediate PDCP SN assignment’ operation which has been suspended.If the condition 1 is fulfilled, this means that the PDCP PDU has notbeen transmitted for relatively long duration and, if the PDCP PDUtransmission is resumed and at least one PDCP PDU is transmitted to thepeer PDCP entity successfully, the HFN error does not occurs.Accordingly, the PDCP condition 2 may be defined as follows.

[PDCP Condition 2]

After PDCP condition 1 is fulfilled, the number of PDCP PDUs transferredto the low layer is greater than threshold 3.

The threshold 3 may be determined depending on the mode of the connectedRLC entity. If an RLC AM entity is connected, the threshold 3 may be setto a relatively low value, e.g. 1 or 2, because the RLC AM providesreliable transmission service. If an RLC UM entity is connected, it ispreferred to set the threshold 3 to a value greater than that.

[Another PDCP Condition 2]

After PDCP condition 1 is fulfilled, the lower layer checks thesuccessful transmission of at least one PDCP PDU among the PDCP PDUstransferred to the lower layer.

If the PDCP condition 2 is fulfilled, the UE assigns a PDCP sequencenumber to the packet and decipher the packet at step 1920.

Sixth Embodiment

The power control of the UE becomes important more and more. Large partof power consumption of the UE occurs in uplink transmission. Therefore,it is very important to minimize unnecessary uplink transmission.

Part of uplink transmission has the following properties.

-   -   Information for assisting scheduling other than actual user data    -   Periodic transmission at a predetermined interval    -   Information useful in the course of active data transmission but        having low usability when there is no data communication

The CQI and SRS transmissions are representative examples. The periodicCQI or SRS transmission is performed by the UE autonomously at apredetermined interval. If the eNB determines that there is no datatransmission to the UE during a long period, it is necessary for the UEto stop autonomous transmission.

In order to accomplish this, the present invention proposes a new MAC CE(hereinafter, referred to as first MAC CE). The first MAC CE includes abitmap having a predetermined size. Each bit of the bitmap correspondsto the serving cell identifier or TAG one by one. If the first MAC CE isreceived, the UE operates as follows.

-   -   If a bit corresponding to the PCell is set to a predetermined        value, the UE stops CQI and SRS transmissions in the PCell.    -   If a bit corresponding to an SCell is set to a predetermined        value, the UE stops SRS transmission in the SCell.    -   If a bit corresponding to the P-TAG is set to a predetermined        value, the UE stops CQI and SRS transmission in the PCell and        SRS transmission in the SCells belonging to the P-TAG.    -   If a bit corresponding to an S-TAG is set to a predetermined        value, the UE stops SRS transmission in the serving cells        belonging to the S-TAG.

The UE restarts the CQI and SRS transmissions as follows.

[Transmission Restart Condition]

-   -   If a PDCCH control information requesting for aperiodic CQI        transmission is received, the UE restarts periodic CQI        transmission in the PCell.    -   If a PDCCH control signal requesting for aperiodic SRS        transmission in a predetermined serving cell and if periodic SRS        transmission is configured to the serving cell, the UE restarts        periodic SRS transmission.

The PDCCH control signal requesting for aperiodic CQI transmission isthe uplink transmission resource allocation control message of which apredetermined field (CQI-request) is set to a predetermined value.

The PDCCH control signal requesting for aperiodic SRS transmission isthe transmission resource allocation control message of which anotherpredetermined field is set to a predetermined value.

FIG. 20 shows a UE operation.

The UE receives the first MAC CE at step 2005. The UE checks apredetermined field (Logical Channel Identifier (LCID)) of the MACheader corresponding to the MAC CE to determine whether the MAC CE isthe first MAC CE.

The UE checks the bitmap of the first MAC CE to stop the periodic SRStransmission in the indicated serving cell at step 2010. If theindicated serving cell is the PCell, the UE stops the periodic CQItransmission. At this time, the UE maintains the periodic CQI and SRSconfiguration information. Also, in order to minimize battery powerconsumption, if the current DRX cycle is the short DRX cycle, the UEtransitions to the long DRX cycle. In order to accomplish this, the UEdetermines whether the drxShortCycleTimer is running and, if so, stopsthe drxShortCycleTimer.

The UE monitors to determine whether the transmission restart conditionis fulfilled and, if the transmission restart condition is fulfilled ina predetermined serving cell, the UE restarts the periodic CQI or SRStransmission at step 2020.

Seventh Embodiment

FIG. 21 shows a DRX operation.

DRX is a technique to minimize the power consumption of the UE in thenon-Active Time by monitoring Physical Downlink Control Channel (PDCCH)and transmitting Channel Status Indicator/Information (CSI) and SoundingReference Signal (SRS) in a predetermined period called Active Time.

The Active Time occurs at every DRX cycle, and the period of Active Timeis applied differently depending on the traffic condition of the UE. Forexample, if a predetermined condition is fulfilled, the UE uses a shortcycle called short DRX cycle 2105 and, otherwise if the condition is notfulfilled, a long cycle called long DRX cycle 2110.

At every DRX cycle, the Active time having a relatively short durationcalled onDuration 2115 starts and, if new data is scheduled in thisduration, the Active Time is extended with the inactivityTimer asdenoted by reference number 2120. The inactivityTimer starts or restartswhenever new data is scheduled and, if the UE traffic is large, extendsthe active time correspondingly.

The CSI means the feedback related to the downlink channel quality suchas Channel Quality Indicator (CQI) and Rank Indicator (RI) and MIMOoperation and is transmitted through Physical Uplink Control Channel(PUCCH) or Physical Uplink Shared Channel (PUSCH). Typically, CSI meansCQI and, in this embodiment, the terms CSI and CQI are usedinterchangeably. The UE can be configured to transmit CSI through apredetermined PUCCH transmission resource at a predetermined intervaland, if the UE transmits CSI on the indicated PUCCH transmissionresource, this is referred to as CSI on PUCCH. If PUSCH (or uplinkchannel for user data or MAC PDU transmission) transmission is scheduledin a subframe for CSI on PUCCH, the UE transmits CSI using a part of thePUSCH transmission resource to comply with the single carriertransmission rule, this is referred to as CSI on PUSCH.

According to the current standard, when the Active Time ends or extendedabruptly, the UE may fall into the situation where it cannot control theCSI/SRS transmission during a certain period. For example, if the ActiveTime ends abruptly, although it is necessary to stop CSI/SRStransmission, the UE cannot to stop the transmission.

In order to solve this problem, degree of freedom for CSI/SRStransmission is granted to the UE during a predetermined period when theActive Time is ended or extended. However, this causes a problem ofcoercing the eNB into so-called double decoding. For example, the eNBperforms decoding once under the assumption that the signal transmittedby the UE is not CSI/SRS transmission and then decoding again under theassumption that the CSI/SRS has been transmitted. The present inventionproposes a method of allowing for CSI/SRS transmission when the CSI/SRStransmission is overlapped with the HARQ feedback or PUSCH transmissionduring n subframes after abrupt expiry of the Active Time and grantingdegree of freedom for CSI/SRS transmission when the CSI/SRS transmissionis not overlapped with the HARQ feedback or PUSCH transmission.

FIG. 22 shows the UE operation related to CSI transmission when theActive Time is terminated.

FIG. 22 shows the UE operation according to the first embodiment.

The UE receives DRX configuration information and CSI configurationinformation at a certain timing from the eNB at step 2205. The DRXconfiguration information includes DRX cycle length, DRX start timecalculation information, onDuration length, and inactivityTimer length.

The CSI configuration information includes the information as follows.

-   -   CQI transmission time information in the form of an index. For        example, the cycle and offset mapped to an index x is        predetermined such that only the index is provided.    -   Information on CQI transmission resource    -   Indicator indicating whether to allowing for simultaneous        transmission of CQI and HARQ ACK/NACK        (simultaneousAckNackAndCQI)

If the above information is received, the RRC of the UE transfers theinformation to the MAC control entity. The MAC control entity of the UEperforms normal DRX operation and CQI transmission operation based onthe control information at step 2210. That is, the MAC control entitydetermines whether it is Active Time at every subframe and, if it is theActive Time, monitors PDCCH and, if the CQI transmission is configured,performs CQI transmission. In the present invention, if the CQItransmission is configured in a certain subframe, this means thatperiodic CQI transmission is scheduled in the subframe. if the ActiveTime ends unexpectedly in the course of the normal DRX operation at step2215, the procedure goes to step 2220. If the Active Time endsunexpectedly, this means that one of the following two situations hasoccurred. For explanation convenience, it is assumed that the subframeat which the Active Time ends unexpectedly is m (sf [m]) hereinafter.

1. The Discontinuous Reception MAC Control Element (DRX MAC CE) isreceived at the UE which maintains the Active time because theonDurationTimer or DRX-inactivityTimer is running.

2. The PDCCH indicating HARQ retransmission is received at the UE whichmaintains the Active Time because the HARQ retransmission timer isrunning.

The DRX MAC CE is the MAC control information transmitted from the eNBto the UE to instruct the UE to stop the onDuration timer andinactivityTimer. The Active time may be started and maintained forvarious reasons of which most normal reason is that one of the above twotimers is running. Accordingly, if the DRX MAC CE is receivedfrequently, this may entail the termination of the Active Time. If theActive time is maintained for other reasons than the running of the twotimers, the UE does not stop the Active Timer although the DRX MAC CE isreceived.

The HARQ retransmission timer is the timer for the UE to receive theHARQ retransmission such that the UE maintains the Active Time while thetimer is running. If the Active Time is maintained for other reasonsthan the running of the HARQ retransmission timer, the UE does not stopthe Active Time although the DRX MAC CE is received.

The UE determines whether periodic CQI transmission during apredetermined number of subframes or through PUCCH is scheduled afterthe unexpected termination of the Active Time at step 2220. If no CQItransmission is scheduled, the UE stops the periodic PUCCH transmissionor CQI transmission on PUCCH before the next Active Time at step 2225.

If the CQI transmission on PUCCH is scheduled between sf [m+1] and sf[m+n], the procedure goes to step 2230. Here, n denotes a parameterdetermined in consideration of the processing capability of the UE andset to a relatively large value, e.g. about 4, so as to be applied toall the UEs including the UEs having low processing capability.

If n is 4, this means that all of the UEs have to stop CQI transmissionafter at least 4 subframes since the end of the Active Time. Forexplanation convenience, the subframe at which CQI transmission isscheduled is sf [x] among the subframes sf [m+1]˜sf [m+n].

The UE determines whether HARQ feedback or PUSCH transmission isscheduled in sf [x] at step 2230. For example, if the HARQ NACK oruplink grant indicating initial transmission or retransmission isreceived at sf [x−1], the UE transmits HARQ feedback (HARQ ACK/NACK orHARQ AN) at sf [x].

If neither HARQ feedback transmission nor PUSCH transmission isscheduled in sf [x], the procedure goes to step 2235. If only the HARQfeedback transmission is scheduled in sf [x], the procedure goes to step2240. If both the HARQ feedback and PUSCH transmissions are scheduled oronly PUSCH transmission is scheduled, the procedure goes to step 2245.

If the procedure goes to step 2235, this means that although the UEperforms CQI transmission on PUCCH during the subframes sf [m+1]˜sf[m+n]this does not compel the eNB to perform double decoding. Accordingly,the UE performs CQI transmission at sf [x] on a best effort basis. Thatis, the UE recognizes the termination of the Active Time and maintainsthe CQI transmission until the subframe at which the CQI transmission issupposed to be terminated arrives.

If the procedure goes to step 2240, this means that both the CQI andHARQ AN transmissions are scheduled in sf [x] and the eNB knows that theUE is transmitting the HARQ AN but does not know whether the UE istransmitting the CQI. For example, the eNB does not know whether the UEdetects the expiry of the Active Time so as to transmit only the AN ordoes not detect yet so as to try to transmit both the CQI and AN. The UEknows that if the sf [x] falls in Active Time it is necessary to sendboth the CQI and AN already before 4 subframes. If sf [x−4] falls in theActive Time, it is preferred to preventing the eNB from doing doubledecoding by transmitting both the CQI and HARQ AN simultaneously at sf[x] in consideration that the probability in which sf [x] falls inActive time is greater than the probability in which sf [x] falls innon-active time. Also it is preferred that if sf [x−4] falls in ActiveTime the eNB performs decoding under the assumption that the UEtransmits both the CQI and AN simultaneously regardless whether sf [x]falls in Active Time. The UE determines whethersimultaneousAckNackAndCQI is set to TRUE at step 2240. If this parameteris set to FALSE, the procedure goes to step 2250. If thesimultaneousAckNackAndCQI is set to False, this means that when the ANand CQI transmissions collide in the same subframe the eNB commands theUE to give up CQI transmission and transmit only the AN to maintain theproperty of single carrier transmission of the UE. Accordingly, at thisstep, since the UE has determined to give up CQI transmission alreadybefore 4 subframes, unexpected termination of Active Time does not causeany problem related to the CQI transmission, and the UE give up CQItransmission and transmits the AN at sf [x].

If the simultaneousAckNackAndCQI is set to TRUE, the UE transmit the CSIand AN at sf [x] at step 2255. In detail, the UE selects a PUCCH formatcapable of transmitting both the CSI and AN using the resource allocatedfor CSI transmission, generates the PUCCH signal in the selected PUCCHformat, and transmits the PUCCH signal at sf [x]. The PUCCH format fortransmitting both the CSI and AN may be any of PUCCH formats 2 a, 2 b,and 3. The PUCCH formats are specified in 36.213 and 36.211. Althoughthe UE does not recognize that the sf [x] falls in Active Time due toits low processing capability, the UE performs the operation necessary,at sf [x−4], for transmitting both the CSI and AN in consideration thatsf [x] is likely to fall in Active Time because the sf [x−4] falls inActive time.

If the procedure goes to step 2245, this means that the UE knows at sf[x−4] that PUSCH and CQI or PUSCH, CQI, and AN have to be transmittedsimultaneously at sf [x]. If sf [x−4] falls in Active Time, sf [x] islikely to fall in Active Time. Accordingly, the UE performs, at sf[x−4], a procedure for transmitting the PUSCH and CQI simultaneously orPUSCH, CQI, and AN simultaneously. In detail, the UE diverts a part ofthe PUSCH transmission resource to transmit the CQI or both the CQI andAN. Which part of the transmission resource is to be diverted isspecified in the standard. Also, the eNB decodes PUSCH under theassumption that if sf [x−4] falls in Active time the UE transmits theCQI or both the CQI and AN using PUSCH at sf [x] in consideration thatsf [x] is likely to fall in Active Time.

In sf [x], the uplink signal such as Scheduling Request (SR) as well asPUSCH and AN may be scheduled. If a plurality of serving cells isconfigured, the PUSCH or SRS of other serving cells may be scheduled insf [x]. At this time, the SR transmission also may influence the CQItransmission. Meanwhile, the PUSCH or SRS transmission of a serving cellother than PCell does not influence the CQI transmission of the PCell.FIG. 25 shows the UE operation thereof.

Step 2505 is similar to step 2205. At step 2505, however, it isdifferent that the SR transmission resource information may beconfigured to the UE. SR is the signal for the UE to request the eNB fortransmission resource allocation. The eNB may allocate the resource fortransmitting 1-bit SR to the UE in PUCCH region and, if new data with ahigh priority occurs, the UE transmits the SR using the SR transmissionresource configured in the PUCCH region.

Step 2510 is identical with step 2210.

Step 2515 is identical with step 2215.

Step 2520 is identical with step 2220.

Step 2525 is identical with step 2225.

The UE determines whether other uplink transmission of the PCell isscheduled in sf [x] and, if so, the procedure goes to step 2540 and,otherwise, step 2535. PCell is a specific serving cell among the pluralserving cells configured to the UE and likely to be the serving cellwhich was the serving cell of the UE before Carrier Aggregation (CA) isconfigured. The serving cells configured to the UE are sorted into PCelland SCell that are characterized as follows in view of uplinktransmission.

PCell: To support PUSCH, PUCCH, and SRS transmissions.

SCell: To support PUSCH and SRS transmission but not PUCCH transmission.

The PUCCH carries CQI, AN, and SR.

Other uplink transmissions of the PCell include AN transmission, SRtransmission, PCell SRS transmission, and PCell PUSCH transmission withthe exception of CQI transmission.

For example, if the HARQ NACK corresponding to the PCell PUSCH or uplinkgrant indicating initial transmission or retransmission in the PCell atsf [x−4], the UE performs PCell PUSCH transmission at sf [x]. If thePDSCH is received through at least one serving cell among the servingcells including the PCell at sf [x−4], the UE transmit HARQ feedback(HARQ ACK/NACK or HARQ AN) at sf [x]. For reference, the PCell PUSCHtransmission is performed only when the uplink grant to (or for) thePCell is received, but the AN is transmitted through the PCell althoughthe PDSCH is received through a serving cell which is not the PCell.

If the procedure goes to step 2535, this means that although the UE hastransmitted CQI on PUCCH in the subframes sf [m+1]˜sf[m+n] and the eNBdoes not compelled to perform double decoding. Accordingly, the UEtransmit CQI at sf [x] on a best effort basis. That is, the UErecognizes the termination of the Active Time and maintains the CQItransmission until the subframe at which the CQI transmission issupposed to be terminated arrives.

If the procedure goes to step 2540, this means that the UE has toperform the CQI transmission along with other uplink transmission at sf[x] of the PCell. Typically, the other uplink transmission is scheduledbefore at least 4 subframes, the UE knows at least at sf [x−4] that theCQI and other uplink transmissions have to be performed simultaneously.If sf [x−4] falls in Active Time, sf [x] is also likely to fall inActive time. Accordingly, the UE the UE performs a procedure at sf [x−4]for transmitting the CQI and other uplink signal of the PCell. Indetail, the UE diverts a part of the PUSCH transmission resource totransmit the CQI or both the CQI and AN or selects the PUCCH formatcapable of transmitting both the CQI and other uplink signal andgenerates the PUCCH signal. Also, the eNB decodes PUSCH under theassumption that if sf [x−4] falls in Active time the UE transmits theCQI or both the CQI and AN using PUSCH at sf [x] in consideration thatsf [x] is likely to fall in Active Time.

FIG. 23 shows the UE operation related to SRS transmission when theActive Time ends.

The UE receives DRX configuration information and type 0 SRSconfiguration information from the eNB at a certain time point at step2305. The type 0 SRS is the SRS transmitted periodically for arelatively long time and include the following configurationinformation. For reference, type 1 SRS is the SRS which is transmittedby the eNB through PDCCH to command transmission as much aspredetermined number of time in a short period unlike the type 0 SRS.

-   -   Dedicated SRS transmission bandwidth    -   The SRS transmission time information is given in the form of an        index.

In more detail, the SRS is transmitted at the last OFDM symbol of asubframe across a predetermined transmission bandwidth. The frequencyresource of a subframe includes PUCCH transmission resource region 2405and PUSCH transmission resource region 2410. One subframe consists of apredetermined number of OFDM symbols, and the SRS transmission resource2420 may be configured at part or whole of the PUSCH transmissionresource of the last symbol 2415. The SRS transmission resource isconfigured to predetermined frequency resources, and the entirebandwidth 2425 of the SRS transmission resource is broadcast through thesystem information. The UE transmits SRS through part or whole of theSRS transmission bandwidth and this is given as the dedicated SRStransmission bandwidth information of the RRC control message.

The UE determines the subframe and frequency resource therein fortransmitting SRS using the SRS transmission time information anddedicated transmission bandwidth information.

If the DRX configuration and type 0 SRS configuration information isreceived, the RRC of the UE sends the above information to the MACcontrol entity of the UE. The MAC control entity of the UE performs thenormal DRX operation and type 0 SRS transmission operation by applyingthe above control information at step 2310. That is, the MAC controlentity determines whether every subframe falls in Active Time and, ifso, monitors PDCCH and, of the type 0 SRS transmission is configured,transmits SRS using a predetermined transmission resource of the lastsymbol. If the type 0 SRS transmission is configured in a subframe, thismeans the type 0 SRS transmission is scheduled in the subframe accordingto the type 0 SRS configuration information. If the Active Time isterminated unexpectedly in the course of the normal DRX operation atstep 2315, the procedure goes to step 2320. For explanation convenience,it is assumed that the Active time is terminated unexpectedly at sf [m].

At step 2320, the UE determines whether type 0 SRS transmission isscheduled during a predetermined number of subframes after theunexpected termination of the Active Time. If not scheduled, the UEsuspends the type 0 SRS transmission to the next Active time at step2325.

If the type 0 SRS transmission is scheduled in the subframes sf [m+1] sf[m+n], the procedure goes to step 2330. Here, n is a parameterdetermined in consideration of the processing capability of the UE andset to a relatively large value, e.g. about 4, so as to be applied allthe UEs including the UEs having low processing capabilities.

If n is 4, this means that all of the UEs have to stop type 0 SRStransmission after at least 4 subframes since the end of the ActiveTime. For explanation convenience, the subframe at which type 4 SRStransmission is scheduled is sf [x] among the subframes sf [m+1]˜sf[m+n].

The UE determines whether the PUSCH transmission is scheduled in sf [x]at step 2330. For example, if an HARQ NACK or an uplink grant indicatinginitial transmission or retransmission is received at sf [x−4], the UEtransmits PUSCH at sf [x].

If no PUSCH transmission is scheduled in sf [x], the procedure goes tostep 2335 and, otherwise if PUSCH transmission is scheduled in sf [x],step 2340.

If the procedure goes to step 2335, this means that although the type 0SRS transmission which should be suspended is in the subframes sf[m+1]˜sf[m+n] is performed the eNB is not compelled to perform doubledecoding. Accordingly, the UE performs type 0 SRS transmission on thebest effort basis at sf [x]. That is, the UE recognizes the terminationof the Active Time and maintains the type 0 SRS transmission until thesubframe at which the type 0 SRS transmission is supposed to beterminated arrives.

If the procedure goes to step 2340, this means that both the type 0 SRSand PUSCH transmissions are scheduled in sf [x] and the eNB knows thatthe UE is transmitting the PUSCH but does not know whether the UE istransmitting the type 0 SRS. For example, the eNB does not know whetherthe UE detects the expiry of the Active Time so as to transmit only thePUSCH or does not detect yet so as to transmit both the PUSCH and type 0SRS. The UE knows that if the sf [x] falls in Active Time it isnecessary to send both the PUSCH and type 0 SRS already before 4subframes. Accordingly, if sf [x−4] falls in the Active Time, it ispreferred to preventing the eNB from doing double decoding bytransmitting both the PUSCH and type 0 SRS simultaneously at sf [x] inconsideration that the probability in which sf [x] falls in Active timeis greater than the probability in which sf [x] falls in non-activetime. Also, it is preferred that if sf [x−4] falls in Active Time theeNB also performs decoding under the assumption that the UE transmitsboth the PUSCH and type 0 SRS simultaneously regardless whether sf [x]falls in Active Time. The UE determines whether the PUSCH is transmittedon the SRS frequency band or non-SRS frequency band at step 2340. Forexample, if the PUSCH transmission resource is allocated on the non-SRStransmission band 2430, the procedure goes to step 2355 and, otherwiseif the PUSCH transmission resource is overlapped with the SRStransmission band 2425 at least in part, step 2350.

The UE transmits PUSCH through all the symbols with the exception of thelast symbol in which type 0 SRS transmission is performed on the besteffort basis. Since the PUSCH transmission is scheduled on the type 0SRS transmission band, the PUSCH transmission is performed in all thesymbols with exception of the last symbol regardless whether the UEtransmits type 0 SRS or not and thus the eNB does not need to performdouble decoding to receive the PUSCH.

If the procedure goes to step 2355, this means that although the SRSshould not be because sf [x] does not fall in Active Time the UE mayknow this or not. If the expiry of the Active Time is recognized, the UEtransmits PUSCH even in the last symbol and, otherwise, SRS instead ofPUSCH. This is the reason for the eNB to perform double decoding toprepare for both the cases. In order to avoid this, the presentinvention proposes transmitting PUSCH and SRS simultaneously regardlesswhether sf [x] falls in Active time or not because sf [x] is likely tofall in Active Time if sf [x−4] falls in Active Time. Accordingly, theUE transmits PUSCH in the symbols with the exception of the last symbolin which SRS is transmitted.

In sf [x], other uplink signal such as Scheduling Request (SR) may bescheduled along with PUSCH and AN. If a plurality of serving cells isconfigured, the PUSCH or SRS of other serving cells may be scheduled insf [x]. At this time, the SR transmission also may influence the SRStransmission of the PCell. Meanwhile, the PUSCH or SRS transmission of aserving cell other than PCell does not influence the SRS transmission ofthe PCell. FIG. 26 shows the UE operation thereof.

Step 2605 is similar to step 2305. At step 2605, however, it isdifferent that the SR transmission resource information may beconfigured to the UE. SR is the signal for the UE to request the eNB fortransmission resource allocation. The eNB may allocate the resource fortransmitting 1-bit SR to the UE in PUCCH region and, if new data with ahigh priority occurs, the UE transmits the SR using the SR transmissionresource configured in the PUCCH region.

Step 2610 is identical with step 2310.

Step 2615 is identical with step 2315.

The UE determines whether at least one type 0 SRS transmission isscheduled in a predetermined number of subframes after the Active Timeis terminated unexpectedly at step 2620. If no type 0 SRS transmissionis scheduled in any serving cell, the UE suspends type 0 SRStransmission to the next Active Time at step 2625. If there is at leastone serving cell in which type 0 SRS transmission is scheduled, theprocedure goes to step 2630.

Step 2625 is identical with step 2325.

The UE determines whether other uplink transmission is scheduled in theserving cell in which type 0 SRS transmission is scheduled at sf [x] atstep 2630 and, if so, the procedure goes to step 2640 and, otherwise,step 2635. If the serving cell in which type 0 SRS transmission isscheduled is the PCell, the other uplink transmission includes the PCellPUSCH transmission and PUCCH transmission including CQI. If the servingcell in which type 0 SRS transmission is scheduled is an SCell, theother uplink transmission means PUSCH transmission in the correspondingSCell.

Step 2635 is identical with step 2335.

If the procedure goes to step 2640, this means that the UE has toperform other uplink transmission along with type 0 SRS transmission atsf [x] in the corresponding serving cell. Typically, the other uplinktransmission is scheduled before at least 4 subframes, the UE knows atsf [x−4] already that the type 0 SRS transmission and other uplinktransmission have to be performed simultaneously. If sf [x−4] falls inActive Time, sf [x] is also likely to fall in Active Time. Accordingly,the UE prepares for the procedure for transmitting type 0 SRS and otheruplink signal of the serving cell in advance at sf [x−4]. In moredetail, if the serving cell is the PCell, the UE selects a transmissionformat capable of transmitting the type 0 SRS and other uplink signalsimultaneously. Depending on the case, if it is impossible to performthe simultaneous transmission, it may be possible to give up the type 0SRS transmission according to a predetermined rule. For example, ifPUSCH transmission is scheduled but no PUCCH transmission format capableof simultaneous transmission of PUCCH and SRS is configured, the UE maygive up SRS transmission and transmit PUCCH. If it is not the case togive up the SRS transmission according to the predetermined rule, the UEtransmits type 0 SRS and PUSCH simultaneously. If the serving cell is anSCell, the UE transmits type 0 SRS and PUSCH simultaneously. That is,the UE transmits PUSCH in the symbols without exception of the lastsymbol in which type 0 SRS is transmitted.

FIG. 33 shows another UE operation.

Typically, the UE transmits CSI on PUCCH during the Active Time, the eNBmay send the UE an RRC control message having a bit called cqi-Mask toinstruct the UE to transmit CSI on PUCCH only in onDuration for moreefficient PUCCH transmission resource management.

Here, onDuration occurs in every short DRX cycle or long DRX cycleaccording to the DRX cycle at the corresponding time point. Accordingly,the UE has to know the DRX cycle at the corresponding time point is theshort DRX cycle of the long DRX cycle correctly. However, the UE mayfail to check the DRX cycle correctly. For example, if the DRX cycle ischanged from the long DRX cycle to the short DRX cycle at a time pointunexpectedly or in a situation where the short DRX cycle is maintain dueto an event occurring at subframe [n-m] (m is small enough) although theUE has predicted the change to the long DRX cycle at subframe [n],onDuration may occur or disappear due to the unexpected event. At thistime, the UE may fail transmitting CSI on PUCCH in the new onDuration orcancelling CSI on PUCCH transmission in the abruptly disappearedonDuration.

In order to overcome the above problem, the present invention proposes amethod for controlling transmission of CSI on PUCCH depending on whetheronDuration is determined at the time before m subframes other thancontrolling the transmission of CSI on PUCCH in the actual onDuration.In this way, when the onDuration occurs or disappears unexpectedly, theUE and the eNB predict the transmission of CSI on PUCCH correctly. Here,m may be 4.

Step 3305 is similar to step 2205. At step 3305, however, it isdifferent that a CQI-mask may be set up to the UE. If the CQI-mask isset up, the UE transmits CQI on PUCCH only in the onDuration with someexceptional situations. If no CQI-mask is set up, the UE transmits CQIin the Active Time with some exceptional situations.

The UE performs a normal DRX operation at step 3310. The UE determineswhether CSI on PUCCH is present at in sf [n] at step 3315.

At step 3315, the UE determines whether a CQI-mask is set up (whetherthe CQI-mask is set up by the upper layer in view of the MAC entity).

If no CQI-mask is set up, the procedure goes to step 3320.

If the CQI-mask is set up, the procedure goes to step 3325.

The UE determines whether sf [n+m] falls in Active Time at step 3320. Ifso, the procedure goes to step 3330. Otherwise, the procedure goes tostep 3323. If it is predicted at sf [n] that sf [n+m] falls in ActiveTime, this means the following cases.

-   -   drx-InactivityTimer is running at sf [n] and ongoing        drx-InactivityTimer is not expired    -   onDurationTimer is running at sf [n+m] when current or        near-future DRX cycle (before sf [n+m]) is applied    -   It is necessary to check PDCCH indicating adaptive        retransmission at sf [n+m] in consideration of ongoing HARQ        operation    -   It is possible for HARQ retransmission Timer is running at sf        [n+m]    -   It is necessary to monitor PDCCH at sf [n+m] for random access        procedure

If the procedure goes to step 3323, this means that it is predicted thatsf [n+m] does not fall in Active Time. However, if it is Active Time andsf [n+m] falls in Active time unexpectedly, this may cause theaforementioned problem in which the UE may not prepare the Active Timeoccurring abruptly and thus, if HARQ A/N or SR on PUCCH or PUSCHtransmission is scheduled at sf [n+m], the UE transmits CSI on PUCCH toprevent the eNB from being compelled to perform double decoding.Accordingly, the UE determines whether sf [n] falls in Active Time andany uplink transmission such as HARQ A/N, SR, and PUSCH is scheduled inthe corresponding serving cell at sf [n+m] at step 3323. If both the twoconditions are fulfilled, the procedure goes to step 3330. If at leastone of the two condition is not fulfilled, i.e. if sf [n] does not fallin Active Time or if no other uplink transmission is scheduled in sf[n+m] although sf [n] falls in Active time, the procedure goes to step3335. If whether sf [n+m] falls in Active Time is determined at sf [n],the prediction reliability is very high although not perfect. The moreimportant thing is that the UE and the eNB make the same decision ontransmission of CSI on PUCCH by determining whether a subframe falls inActive Time before m subframes in advance.

The UE determines whether sf [n+m] falls in Active Time at step 3325.That is, the UE determines whether the onDurationTimer is running at sf[n+m] when the DRX cycle predicted to be applied in the near future. Ifso, the procedure goes to step 3330 and, otherwise, step 3335.

At step 3335, the UE does not transmit CSI on PUCCH although the CSI onPUCCH is scheduled at sf [n+m].

At step 3330, if CSI on PUCCH is scheduled at sf [n+m], the UE transmitsCSI on PUCCH.

FIG. 34 shows the UE operation simplified by modifying FIG. 33 a little.

Step 3405 is identical with step 3305.

Step 3410 is identical with step 3310.

Step 3415 is identical with step 3315.

If it is predicted that sf [n+m] falls in Active Time at step 3420, theprocedure goes to step 3430 and, otherwise, step 3435. That is, whetherto transmit CSI on PUCCH at current subframe is determined depending onthe UE prediction, made before m subframes, about whether the currentsubframe falls in Active Time.

If CSI on PUCCH is scheduled in sf [n+m], the UE transmits CSI on PUCCHat step 3430.

At step 3435, the UE does not transmit CSI on PUCCH at sf [n+m]. Thatis, if it is determined before m subframes that the current subframedoes not fall in Active Time, the UE does not transmit CSI on PUCCHalthough sf [n+m] falls in Active Time and CSI on PUCCH is scheduledtherein actually.

The UE determines whether sf [n+m] falls in onDuration at step 3425. TheUE determines whether the onDurationTimer is running at sf [n+m] whenthe DRX cycle predicted to be applied in the near feature. If so, theprocedure goes to step 3335 and, otherwise, step 3330. If it isdetermined that the onDurationTimer is running at sf [n+m] when the DRXcycle applied at sf [n] is applied, the procedure goes to step 3440. Ifit is determined that the onDurationTimer is not running at sf [n+m],the procedure goes to step 3435. That is, if it is predicted at sf [n]that sf [n+m] falls in onDuration, the procedure goes to step 3430 and,otherwise, step 3435.

The start time of the onDurationTimer is determined by followingequation, and the size of the onDurationTimer is configured by the eNBto the UE.

In the case that the short DRX cycle is applied, the onDurationTimerstarts at the subframe fulfilling the following equation.

[(SFN*10)+subframe number] modulo (shortDRX−Cycle)=(drxStartOffset)modulo (shortDRX−Cycle)

In the case that the long DRX cycle is applied, the onDurationTimerstarts at the subframe fulfilling the following equation.

[(SFN*10)+subframe number] modulo (longDRX−Cycle)=drxStartOffset:

At step 3430, if CSI on PUCCH is scheduled in sf [n+m], the UE transmitsthe CSI on PUCCH.

At step 3435, the UE does not transmit CSI on PUCCH at sf [n+m]. Thatis, if it is determined before m subframes that the current subframedoes not fall in onDuration, the UE does not transmit CSI on PUCCHalthough sf [n+m] falls in onDuration and CSI on PUCCH is scheduledtherein actually. If CSI on PUCCH is not transmitted, this may includedropping scheduled CSI on PUCCH.

Eighth Embodiment

The present invention relates to a method and apparatus for transmittingan RLF report including useful UTRAN cell information to the E-UTRAcell. Particularly, the present invention proposes a method for the UEto determine to store the useful UTRAN cell information as the RLFreport information in consideration of a specific condition.

Researches are being conducted on the cell service area optimization inthe LTE (E-UTRA) standard under the name of Mobility Robust Optimization(MRO). In the MRO issue, consideration is taken to other Radio AccessTechnologies such as UMTS (UTRAN) as well as the service area of LTEcell.

The RLF report is the Information Element (IE) reporting diverseinformation which the UE has recorded in RLF situation to the eNB. InMRO, the RLF report is used in optimizing the cell service area. In theconventional technology, the RLF report includes the information asfollows.

TABLE 2 RLF-Report-r9 ::= SEQUENCE {  measResultLastServCell-r9 SEQUENCE {   rsrpResult-r9   RSRP-Range,   rsrqResult-r9   RSRQ-Range  OPTIONAL  },  measResultNeighCells-r9  SEQUENCE {  measResultListEUTRA-r9  MeasResu1tList2EUTRA-r9 OPTIONAL,  measResultListUTRA-r9  MeasResu1tList2UTRA-r9 OPTIONAL,  measResultListGERAN-r9  MeasResultListGERAN  OPTIONAL,  measResu1tsCDMA2000-r9  MeasResultList2CDMA2000-r9 OPTIONAL  }OPTIONAL,  ...,  [[ locationInfo-r10  LocationInfo-r10  OPTIONAL,  failedPCellId-r10   CHOICE {    cellGlobalId-r10  CellGlobalIdEUTRA,   pci-arfcn-r10  SEQUENCE {     physCellId-r10  PhysCellId,    carrierFreq-r10  ARFCN-ValueEUTRA    }   } OPTIONAL,  reestablishmentCellId-r10  CellGlobalIdEUTRA  OPTIONAL,  timeConnFailure-r10   INTEGER (0..1023)   OPTIONAL,  connectionFailureType-r10  ENUMERATED {rlf, hof}  OPTIONAL,  previousPCellId-r10   CellGlobalIdEUTRA   OPTIONAL  ]] }

TABLE 3 connectionFailureType This field is used to indicate whether theconnection failure is due to radio link failure or handover failure.failedPCellId This field is used to indicate the PCell in which RLF isdetected or the target PCell of the failed handover.measResultLastServCell This field refers to the last measurement resultstaken in the PCell, where radio link failure happened. previousPCellIdThis field is used to indicate the source PCell of the last handover(source PCell when the last RRC-Connection-ReconfigurationmessageincludingmobilityControlInfowasreceived).reestablishmentCellId This field is used to indicate the cell in whichthe re-establishment attempt was made after connection failure.timeConnFailure This field is used to indicate the time elapsed sincethe last HO initializa- tion until connection failure. Actual value = IEvalue * 100 ms. The maximum value 1023 means 102.3 s or longer.

Among the information, previousPCellID and reestablishmentCellId areidentifiers of specific cell at the time when RLF has occurred. ThepreviousPCellId is the Evolved Cell Global Identifier (ECGI) value ofthe PCell to which the UE is handed over lastly. Meanwhile, thereestablishmentCellId is the ECGI value of the cell to which the UE hastried reestablishment after RLF. These cell information are reported tothe E-UTRA eNB for use in cell service area optimization.

All of the cell information are restricted to the E-UTRA cell.Accordingly, the information on the cell belonging to different RATssuch as UTRAN cell are not associated. Actually, the handover occursfrequently between mobile communication systems. This is referred to asinter-RAT handover. Accordingly, it is necessary to consider other RATsin optimizing the cell service area. It is also required to modify theRLF report restricted to the E-UTRA cell information so as to includethe UTRAN cell information necessary in the optimization procedure,thereby optimizing the cell service area more inclusively.

In the present invention, two useful UTRAN cell information areintroduced, and the UE operation of including this information in theRLF report. The two useful UTRAN cell information are as follows.

1) selectedUTRA-CellID

This UTRAN cell information is the identifier of the UTRAN to which theUE tries to attach after RLF occurrence in the E-UTRA cell.

2) previousUTRA-CellID

This UTRAN cell information is the identifier of the UTRAN cell whichhas served the UE before the inter-RAT handover to the E-UTRA cell.

Among the above UTRAN cell information, the UTRAN cell id may beincluded in the RLF report in the form of global cell identifier orphysical cell identifier of the UTRAN cell. One of the two formats maybe applied according to a predetermined rule. For example,

-   -   if it fails to acquire the global cell identifier of the UTRAN        cell, the UE may include the physical cell identifier in the RLF        report instead. Or    -   if possible, may include both the global cell identifier and        physical cell identifier in the RLF report.

The necessity of UTRAN cell information and UE operation of includingthe cell information in the RLF report are described in differentembodiments in detail.

In this embodiment, a description is made of scenario related to thenecessity of cell information selectedUTRA-CellID. Particularly, thecondition and UE operation for including the cell information in the RLFreport are proposed.

FIG. 27 is a diagram illustrating a scenario related to the cellinformation selectedUTRA-CellID.

The UE 2715 connected to the E-UTRA 2700 experiences RLF 2720 andperforms RRC Connection Reestablishment. At this time, the UE performsmeasurement and records the aforementioned information at the RLFoccurrence time. The UE selects the UTRAN cell 2705 as the cell suitablefor attachment and attempts connection at step 2725. The UE performsinter-RAT handover to the E-UTRA cell 2710 in the connected mode or cellreselection process to the E-UTRA cell in the idle mode at step 2730.The UE connected in the E-UTRA cell reports RLF to the E-UTRA cell atstep 2735. At this time, if the UTRAN cell id of the UTRAN cell 2705 towhich the UE attempts connection after RLF occurrence in the E-UTRA cell2700 is further added as the RLF report information, it is possible toidentify the potential UTRAN cell around at the RLF occurrence time. Itis also possible to determine whether the UE is connected to the E-UTRAcell or UTRAN cell after the RLF. This is the information very useful inthe procedure of optimizing the cell service area afterward. Forexample, it is possible to check the service coverage hole of the E-UTRAcell and whether the coverage hole is covered by the service area of theUTRAN cell.

FIG. 28 is a signal flow diagram illustrating a procedure of includingthe selectedUTRA-CellID.

In the course of data communication with the E-UTRA 2805 at step 2820,the UE 2800 experiences RLF at step 2825. The UE performs RRC ConnectionReestablishment at step 2830. If an inter-RAT cell (i.e., UTRAN cell) isselected as the cell to attempt connection, the UE stores the UTRAN cellid of the selected UTRAN cell as RLF report information at step 2835.The UE connects to the UTRAN cell at step 2840. The UE ends thecommunication and enters the idle mode at step 2845. The UE performssell reselection to the E-UTRA cell at step 2850. The UE attemptsconnection to the E-UTRA cell and sends the eNB an RRC ConnectionRequest message at step 2855. The UE receives an RRC Connection Setupmessage from the eNB at step 2860. The UE sends the eNB an RRCConnection Complete message including an indicator rlf-InfoAvailable tonotify the eNB whether the UE has RLF report at step 2865. Thisindicator is included only when the RPLMN of the current serving cellbelongs to the RPLMN list or ePLMN list at the RLF occurrence time. TheUE receives a UE Information Request message including an indicatorrlf-ReportReq at step 2870. If this indicator is included, the UE has tosend the eNB the RLF report. The UE sends the eNB the RLF report using aUE Information Response message at step 2875.

FIG. 29 is a flowchart illustrating the UE operation of including thecell information selectedUTRA-CellID.

The UE experiences RLF in the connected E-UTRA at step 2900. The UEperforms RRC Connection Reestablishment at step 2905. The UE determineswhether an inter-RAT cell (i.e., UTRAN cell) is selected as a new cellto connect at step 2910. If so, the UE stores the UTRAN cell id of theselected UTRAN cell as RLF report information at step 2915.

Ninth Embodiment

A description is made of the scenario related to the necessity of thecell information selectedUTRA-CellID in this embodiment. Particularly,the condition and UE operation of including the cell information in theRLF report are proposed.

FIG. 30 is a diagram illustrating a scenario related to the cellinformation previousUTRA-CellId.

The UE 3015 connected to the UTRAN 3000 performs inter-RAT handover toan E-UTRA cell at step 3020. The UE completes the inter-RAT handover tothe E-UTRA at step 3025. However, the UE experiences RLF not long afterat step 3030 and performs RRC Connection Reestablishment. At this time,the UE performs measurement and records the aforementioned information.The UE connects to the UTRAN cell again at step 3035. Afterward, the UEperforms inter-RAT handover to the E-UTRA cell 3010 in the connectedmode or the cell reselection procedure to the E-UTRA cell in the idlemode at step 3040. The UE connected to the E-UTRA cell reports RLF tothe E-UTRA cell at step 3045. At this time, if the UTRAN cell id of theUTRAN cell 3000 to which the UE attempts connection after RLF occurrencein the E-UTRA cell 3005 is further added as the RLF report information,it is possible to transfer the RLF report information to the UTRAN cell3000. The RLF report information transferred to the UTRAN cell can beused for solving the mobility problem in the UTRAN cell. In thisscenario, the main cause of the RLF is the inter-RAT handover from theUTRAN cell to the E-UTRA cell is performed too fast (i.e. too earlyhandover).

FIG. 31 is a signal flow diagram illustrating a procedure of includingthe cell information previousUTRA-CellID.

In the course of data communication with the UTRAN 3105 at step 3120,the UE 3100 performs inter-RAT handover to the E-UTRA cell at step 3125.The UE completes the inter-RAT handover at step 3130 and then experienceRLF immediately at step 3135. The UE determines whether an intra-E-UTRAhandover or inter-RAT handover from UTRAN to E-UTRA has been performedbefore the RLF at step 3140. If the inter-RAT handover has occurred, theUE stores the UTRAN cell id of the serving UTRAN cell 3105 before theinter-RAT handover as the RLF report information. Otherwise, the UEstores the legacy previousPCellId. The UE connects to the UTRAN cellagain at step 3145. The UE completes the communication and enters theidle mode at step 3150. The UE performs cell reselection to the E-UTRAcell at step 3155. The UE attempts connection to the E-UTRA cell bytransmitting an RRC Connection Request message at step 3160. The UEreceives an RRC Connection setup message from the eNB at step 3165. TheUE sends the eNB an RRC Connection Setup Complete message including andindicator rlf-InfoAvailable to notify the eNB that the UE has the RLFreport at step 3170. This indicator is included only when the RPLMN ofthe current serving cell belongs to the RPLMN list or ePLMN list at theRLF occurrence time. the UE receives a UE Information Request messageincluding the indicator rlf-ReportReq at step 3175. If this indicator isincluded, the UE has to send the RLF report to the eNB. the UE sends theeNB the RLF report using a UE Information Response message at step 3180.

FIG. 32 is a flowchart illustrating the UE operation of including thecell information previousUTRA-CellID.

The UE experiences RLF in the connected E-UTRA cell at step 3200. The UEdetermines whether the RRC Connection Reconfiguration message includinga mobilityControlInfo IE from the eNB before the RLF occurrence at step3205. If so, the UE determines whether the reconfiguration message is ofinstructing to perform intra-E-UTRA handover at step 3210. If so, the UEstores the legacy previousPCellId as the RLF report information at step3220. Otherwise, the UE determines whether the reconfiguration messageis of instructing to perform inter-RAT handover from UTRAN to E-UTRA atstep 3215. If so, the UE stores the UTRAN cell id of the serving UTRANcell before the inter-RAT handover as the RLF report information at step3225.

FIG. 14 is a block diagram illustrating a configuration of the UEaccording to an embodiment of the present invention.

Referring to FIG. 14, the UE according to an embodiment of the presentinvention includes a transceiver 1405, a controller 1410, amultiplexer/demultiplexer 1420, a control message processor/RRCcontroller 1435, and upper layer processors 1425 and 1430.

The transceiver 1405 is responsible for receiving data and predeterminedcontrol signal through a downlink channel of the serving cell andtransmitting data and predetermined control signals through an uplinkchannel. In the case that a plurality of serving cells is configured,the transceiver 1405 transmits and receives data and control signalsthrough the plural serving cells.

The multiplexer/demultiplexer 1420 is responsible for multiplexing datagenerated by the upper layer processors 1425 and 1430 and the controlmessage processor 1435 or demultiplexing data received by thetransceiver 1405 to deliver the demultiplexed data to the upper layerprocessors 1425 and 1430 and the control message processor 1435.

The control message processor 1430 is an RRC layer entity for processingthe control message received from the eNB to takes a necessary action.For example, the control message processor 1430 receives RRC controlmessage and transfers the SCell information and DRX information to thecontroller. The control message processor also transfers the informationon the SCell and TAG to which the SCell belongs to the controller.

The upper layer processor 1425 and 1430 is established per service. Theupper layer processor processes the data generated in the user servicesuch as File Transfer Protocol (FPT) and Voice over Internet Protocol(VoIP) and transfers the processed data to the multiplexer/demultiplexer1420 or processes the data from the multiplexer/demultiplexer 1420 anddelivers the processed data to the upper layer service applications. Theupper layer processor is made up of an RLC layer entity, a PDCP layerentity, and an IP layer entity.

The control unit 1410 checks the scheduling command, e.g. uplink grants,received through the transceiver 1405 and controls the transceiver 1405and the multiplexer/demultiplexer 1420 to perform uplink transmissionwith appropriate transmission resource at an appropriate timing. Thecontroller 1410 measures and reports the SFN offset and determines theSFN of the target cell by applying the indicated SFN offset. Thecontroller controls the operation related to the adaptiveretransmission. The controller performs the DRX operation and controlsCSI and SRS transmission. The controller also calculates the uplinktransmission power and controls to apply an appropriate uplinktransmission power. The controller also controls the operations ofconfiguring SCells and activating/deactivating the SCells. The controlunit also controls the Radio Frequency Frontend reconfigurationprocedure. The control unit controls the TAG configuration procedure.

FIG. 15 is a block diagram illustrating a configuration of the eNBaccording to an embodiment of the present invention, and the eNBincludes a transceiver 1505, a controller 1510, amultiplexer/demultiplexer 1520, a control message processor/RRCcontroller 1535, upper layer processors 1525 and 1530, and a scheduler1515.

The transceiver 1505 is responsible for transmitting data andpredetermined control signal through a downlink channel and receivingdata and predetermined control signals through an uplink channel. In thecase that a plurality of carriers is configured, the transceiver 1505transmits and receives data and control signals through the pluralcarriers.

The multiplexer/demultiplexer 1520 is responsible for multiplexing datagenerated by the upper layer processors 1525 and 1530 and the controlmessage processor 1535 or demultiplexing data received by thetransceiver 1505 to deliver the demultiplexed data to the upper layerprocessors 1525 and 1530 and the control message processor 1435. Thecontrol message processor 1535 processes the control message transmittedby the UE to take a necessary action or generates a control messageaddressed to the UE to the lower layer.

The upper layer processor 1455 and 1530 is established per service,processes the data to be transmitted to the S-GW or another eNB into RLCPDU and transfers the RLC PDU to the multiplexer/demultiplexer 1520, andprocesses the RLC PDU from the multiplexer/demultiplexer 1520 into PDCPSDU to be transmitted to the S-GW or another eNB.

The scheduler allocates transmission resource to the UE at anappropriate timing in consideration of the buffer state and channelcondition of the UE and processes the signal transmitted form the UE orto be transmitted to the UE.

The controller controls overall operations of configuring SCells andactivating/deactivating the SCells. The controller determines the ActiveTime of the UE in consideration of the DRX operation of the UE andcontrols PDCCH transmission and CSI/SRS reception. The controllercontrols the operation of managing the TAGs. The controller alsocontrols the operation related to SFN offset.

What is claimed is:
 1. A method performed by a terminal in a wirelesscommunication system, the method comprising: receiving, from a basestation, measurement configuration information including measurementtarget information and measurement report trigger information; obtainingsystem frame number (SFN) offset information, in case that the terminalis required to obtain the SFN offset information based on themeasurement configuration information; and transmitting, to the basestation, a radio resource control (RRC) message including the SFN offsetinformation, the SFN offset information including first informationindicating a difference between a first SFN of a first cell and a secondSFN of a second cell and second information indicating a differencebetween a specific timing of the first cell and a specific timing of thesecond cell.
 2. The method of claim 1, wherein the RRC message istransmitted after a predetermined time associated with the SFN offsetinformation.
 3. The method of claim 1, wherein the RRC message istransmitted, in case that the terminal obtains the first information andthe second information.
 4. The method of claim 1, wherein themeasurement configuration information includes information indicating atleast one cell for the measurement for the SFN offset information, andwherein the RRC message further includes a physical cell identity of thesecond cell.
 5. The method of claim 1, wherein the second SFN of thesecond cell is obtained based on master information block (MIB) of thesecond cell.
 6. A method performed by a base station in a wirelesscommunication system, the method comprising: transmitting, to aterminal, measurement configuration information including measurementtarget information and measurement report trigger information; andreceiving, from the terminal, a radio resource control (RRC) messageincluding system frame number (SFN) offset information, the SFN offsetinformation including first information indicating a difference betweena first SFN of a first cell and a second SFN of a second cell and secondinformation indicating a difference between a specific timing of thefirst cell and a specific timing of the second cell, wherein the SFNoffset information is received, in case that reporting for the SFNoffset information is indicated.
 7. The method of claim 6, wherein theRRC message is received after a predetermined time associated with theSFN offset information.
 8. The method of claim 6, wherein the RRCmessage is received, in case that the terminal obtains the firstinformation and the second information.
 9. The method of claim 6,wherein the measurement configuration information includes informationindicating at least one cell for the measurement for the SFN offsetinformation, and wherein the RRC message further includes a physicalcell identity of the second cell.
 10. The method of claim 6, wherein thesecond SFN of the second cell is obtained based on master informationblock (MIB) of the second cell.
 11. A terminal in a wirelesscommunication system, the terminal comprising: a transceiver; and acontroller configured to: receive, from a base station via thetransceiver, measurement configuration information including measurementtarget information and measurement report trigger information, obtainsystem frame number (SFN) offset information, in case that the terminalis required to obtain the SFN offset information based on themeasurement configuration information, and transmit, to the base stationvia the transceiver, a radio resource control (RRC) message includingthe SFN offset information, the SFN offset information including firstinformation indicating a difference between a first SFN of a first celland a second SFN of a second cell and second information indicating adifference between a specific timing of the first cell and a specifictiming of the second cell.
 12. The terminal of claim 11, wherein the RRCmessage is transmitted after a predetermined time associated with theSFN offset information.
 13. The terminal of claim 11, wherein the RRCmessage is transmitted, in case that the terminal obtains the firstinformation and the second information.
 14. The terminal of claim 11,wherein the measurement configuration information includes informationindicating at least one cell for the measurement for the SFN offsetinformation, and wherein the RRC message further includes a physicalcell identity of the second cell.
 15. The terminal of claim 11, whereinthe second SFN of the second cell is obtained based on masterinformation block (MIB) of the second cell.
 16. A base station in awireless communication system, the base station comprising: atransceiver; and a controller configured to: transmit, to a terminal viathe transceiver, measurement configuration information includingmeasurement target information and measurement report triggerinformation, and receive, from the terminal via the transceiver, a radioresource control (RRC) message including system frame number (SFN)offset information, the SFN offset information including firstinformation indicating a difference between a first SFN of a first celland a second SFN of a second cell and second information indicating adifference between a specific timing of the first cell and a specifictiming of the second cell, wherein the SFN offset information isreceived, in case that reporting for the SFN offset information isindicated.
 17. The base station of claim 16, wherein the RRC message isreceived after a predetermined time associated with the SFN offsetinformation.
 18. The base station of claim 16, wherein the RRC messageis received, in case that the terminal obtains the first information andthe second information.
 19. The base station of claim 16, wherein themeasurement configuration information includes information indicating atleast one cell for the measurement for the SFN offset information, andwherein the RRC message further includes a physical cell identity of thesecond cell.
 20. The base station of claim 16, wherein the second SFN ofthe second cell is obtained based on master information block (MIB) ofthe second cell.